diff --git a/@postman/src/main.cpp b/@postman/src/main.cpp
index 06f0045..cbf2254 100644
--- a/@postman/src/main.cpp
+++ b/@postman/src/main.cpp
@@ -49,11 +49,16 @@
 // 'HAVE_CLIENT_I2C'
 // --> i have a client w/ I2C i/f. enable the I2C client task.
 //
+// 'USE_ALTERNATIVE_ADDRESSES'
+// --> peer list limited max. 20.
+//     so, we have alternative address book that covers after 20th.
+//
 //==========</list-of-configurations>==========
 //
 #define HAVE_CLIENT_I2C
 #define DISABLE_AP
 #define REPLICATE_NOTE_REQ
+#define USE_ALTERNATIVE_ADDRESSES
 
 //============<parameters>============
 //
@@ -349,7 +354,11 @@ void setup() {
   // peerInfo.encrypt = false;
   // esp_now_add_peer(&peerInfo);
 
+#if defined(USE_ALTERNATIVE_ADDRESSES)
+  AddressBook * book = lib.getBookByTitle("audioooo alt");
+#else
   AddressBook * book = lib.getBookByTitle("audioooo");
+#endif
   for (int idx = 0; idx < book->list.size(); idx++) {
     Serial.println("- ! (esp_now_add_peer) ==> add a '" + book->list[idx].name + "'.");
 #if defined(ESP32)
diff --git a/audioooo/src/main.cpp b/audioooo/src/main.cpp
index 19d267f..d7ee260 100644
--- a/audioooo/src/main.cpp
+++ b/audioooo/src/main.cpp
@@ -35,10 +35,15 @@
 //   + then, network would be flooded by infinite duplicating msg.,
 //     unless they stop reacting to 'known' req. for some seconds. (e.g. 3 seconds)
 //
+// 'USE_ALTERNATIVE_ADDRESSES'
+// --> peer list limited max. 20.
+//     so, we have alternative address book that covers after 20th.
+//
 //==========</list-of-configurations>==========
 //
 #define DISABLE_AP
 #define REPLICATE_NOTE_REQ
+#define USE_ALTERNATIVE_ADDRESSES
 
 //============<parameters>============
 //
@@ -538,7 +543,11 @@ void setup() {
   // peerInfo.encrypt = false;
   // esp_now_add_peer(&peerInfo);
 
+#if defined(USE_ALTERNATIVE_ADDRESSES)
+  AddressBook * book = lib.getBookByTitle("audioooo alt");
+#else
   AddressBook * book = lib.getBookByTitle("audioooo");
+#endif
   for (int idx = 0; idx < book->list.size(); idx++) {
     Serial.println("- ! (esp_now_add_peer) ==> add a '" + book->list[idx].name + "'.");
     esp_now_peer_info_t peerInfo;
diff --git a/post.h b/post.h
index 6e539a2..d65b1a7 100644
--- a/post.h
+++ b/post.h
@@ -113,18 +113,19 @@ struct AddressLibrary {
       //
       book.add(Address(0xAC, 0x67, 0xB2, 0x0B, 0xAE, 0x0C, "audioooo #1 (Q)")); //WROOM <- sender(the Q injector)
       book.add(Address(0xAC, 0x67, 0xB2, 0x0B, 0xAD, 0xB0, "audioooo #2")); //WROOM
-      book.add(Address(0xA8, 0x03, 0x2A, 0x6C, 0x88, 0x78, "audioooo #3")); //WROVER
-      book.add(Address(0xA8, 0x03, 0x2A, 0x6C, 0x88, 0x5C, "audioooo #4")); //WROVER
-      book.add(Address(0xA8, 0x03, 0x2A, 0x75, 0xD0, 0x68, "audioooo #5")); //WROVER
+      book.add(Address(0xA8, 0x03, 0x2A, 0x6C, 0x88, 0x78, "audioooo #3")); //WROVER (==> audioooo alt)
+      book.add(Address(0xA8, 0x03, 0x2A, 0x6C, 0x88, 0x5C, "audioooo #4")); //WROVER (==> audioooo alt)
+      book.add(Address(0xA8, 0x03, 0x2A, 0x75, 0xD0, 0x68, "audioooo #5")); //WROVER (==> audioooo alt)
       //
       book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB4, 0xDD, "sampler #1")); //TEENSY+ESP8266
       book.add(Address(0xB4, 0xE6, 0x2D, 0x37, 0x37, 0xAE, "sampler #2")); //TEENSY+ESP8266
       book.add(Address(0xEC, 0xFA, 0xBC, 0x63, 0x19, 0x84, "sampler #3")); //TEENSY+ESP8266
       book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB4, 0x19, "sampler #4")); //TEENSY+ESP8266
-      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xBA, 0x44, "sampler #5")); //TEENSY+ESP8266
-      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB5, 0xC2, "sampler #6")); //TEENSY+ESP8266
-      book.add(Address(0xB4, 0xE6, 0x2D, 0x37, 0x09, 0x92, "sampler #7")); //TEENSY+ESP8266
-      book.add(Address(0x68, 0xC6, 0x3A, 0xD5, 0x3E, 0xF3, "sampler #8")); //TEENSY+ESP8266
+      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xBA, 0x44, "sampler #5")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB5, 0xC2, "sampler #6")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0xB4, 0xE6, 0x2D, 0x37, 0x09, 0x92, "sampler #7")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0x68, 0xC6, 0x3A, 0xD5, 0x3E, 0xF3, "sampler #8")); //TEENSY+ESP8266 (==> audioooo alt)
+      // (alternative list)
       book.add(Address(0xB4, 0xE6, 0x2D, 0x37, 0x45, 0xF5, "sampler #9")); //TEENSY+ESP8266
       book.add(Address(0xBC, 0xDD, 0xC2, 0xB2, 0xAF, 0xD4, "sampler #A")); //TEENSY+ESP8266
       book.add(Address(0x84, 0xCC, 0xA8, 0xA3, 0xA7, 0xB5, "sampler #B")); //TEENSY+ESP8266
@@ -136,6 +137,37 @@ struct AddressLibrary {
       // + we have 5 more un-registered devices. esp8266 devices will broadcast for them. hopely all get to contact w/ msg. on time.
       lib.push_back(book);
     }
+    // book #5
+    {
+      AddressBook book = AddressBook("audioooo alt");
+      //
+      book.add(Address(0xAC, 0x67, 0xB2, 0x0B, 0xAE, 0x0C, "audioooo #1 (Q)")); //WROOM <- sender(the Q injector)
+      book.add(Address(0xAC, 0x67, 0xB2, 0x0B, 0xAD, 0xB0, "audioooo #2")); //WROOM
+      book.add(Address(0xA8, 0x03, 0x2A, 0x6C, 0x88, 0x78, "audioooo #3")); //WROVER
+      book.add(Address(0xA8, 0x03, 0x2A, 0x6C, 0x88, 0x5C, "audioooo #4")); //WROVER
+      book.add(Address(0xA8, 0x03, 0x2A, 0x75, 0xD0, 0x68, "audioooo #5")); //WROVER
+      //
+      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB4, 0xDD, "sampler #1")); //TEENSY+ESP8266
+      book.add(Address(0xB4, 0xE6, 0x2D, 0x37, 0x37, 0xAE, "sampler #2")); //TEENSY+ESP8266
+      book.add(Address(0xEC, 0xFA, 0xBC, 0x63, 0x19, 0x84, "sampler #3")); //TEENSY+ESP8266
+      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB4, 0x19, "sampler #4")); //TEENSY+ESP8266
+      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xBA, 0x44, "sampler #5")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0x98, 0xF4, 0xAB, 0xB3, 0xB5, 0xC2, "sampler #6")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0xB4, 0xE6, 0x2D, 0x37, 0x09, 0x92, "sampler #7")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0x68, 0xC6, 0x3A, 0xD5, 0x3E, 0xF3, "sampler #8")); //TEENSY+ESP8266 (==> audioooo alt)
+      // (alternative list)
+      book.add(Address(0xBC, 0xDD, 0xC2, 0x14, 0x75, 0x6F, "huzzah #F")); //TEENSY+HUZZAH (==> audioooo alt)
+      book.add(Address(0xBC, 0xDD, 0xC2, 0x14, 0x63, 0x8E, "huzzah #G")); //TEENSY+HUZZAH (==> audioooo alt)
+      book.add(Address(0xBC, 0xDD, 0xC2, 0x14, 0x74, 0xD2, "huzzah #H")); //TEENSY+HUZZAH (==> audioooo alt)
+      book.add(Address(0x5C, 0xCF, 0x7F, 0xB8, 0xB6, 0x80, "sampler #I")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0xF4, 0xCF, 0xA2, 0xED, 0xB6, 0xEC, "sampler #J")); //TEENSY+ESP8266 (==> audioooo alt)
+      book.add(Address(0x5C, 0xCF, 0x7F, 0xB7, 0x55, 0x98, "sampler #K")); //TEENSY+ESP8266 (==> audioooo alt)
+      //
+      book.add(Address(0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, "BROADCAST"));  //a broadcast ... (unstable.. especially esp32)
+      lib.push_back(book);
+
+
+    }
   }
   //
   AddressBook* getBookByTitle(String title_) {