Somebody please tell me what I can use, at a reasonable cost, to run a Roland PK5 into a Hartke 2115 combo bass amp. I bought an Alesis NanoBass sound module but I can't get it to work with the Roland or anything else.

The PK5 can definatly trigger the nano module .... IF it works properly. Check out both pieces with other gear, but they should be compatible. Make sure the simple things are checked first - midi channels, cables, etc...We tend to overlook the obvious sometimes.