Thank you very much for great post. Unfortunately (based on vogons) seems dosbox does not support share.exe too:(
Connecting with client works, but using share.exe for server is probably problem. For client I tested Telemate, telix and mTcp, but this does not help you:(
I exactly know why you love these games. I played many years game Brutus MUD based on Circle MUD. Based on your post I tried connect to server and it works fine with serial1=modem enabled. These old text games still offer something magical.