!st gen - radio question - no audio - time to replace?

[windrider1983]

I have an 83 stock Venture (no cb or intercom) and the previous owner had installed a standard car radio in place of the original. I replaced it with a Kenwood KRC-38MR with remote control pad several years ago, and it has performed quite well. Then last summer I replaced the cycles' fuse block and rather than run everything off of one accessory feed I inserted a relay (energized by the accessory circuit) and added a secondary fuse block thru which I fed all of the accessories (so I could split out various light circuits separate from the radio circuit). The new radio circuit was fused at 5 amps and was connected to a noise suppressor that was there previously. Everything worked fine when I was testing it in the garage on the accessory position (without the cycle running). The first time I ventured out (no pun intended) and attempted to turn the radio on, I could not hear anything until I stopped - then it was making stuttering sounds, as if it was getting intermittent power in rapid succession. Within a few minutes I got no sound at all - lights are on and it changes stations, etc, but no audio output. Fuses are all intact. The leads to the speakers are reading a constant 6 volts. I verified the voltage going to the radio appears to be constant as far my cheapo voltmeter shows (slightly higher than 12 volts when the engine is running, as I would expect). So the first question is whether anyone has any ideas as to what I have done to the radio itself, and more importantly, is there a flaw in my design of running the radio off of a relay circuit? Am I possibly getting voltage spikes that are somehow filtered thru the accessory circuit, but being reintroduced via the relay?

Assuming I have blown the radio, any suggestions as to a reasonable relacement with an eye for future additions of a GPS, MP3, cell phone and headset interfaces, etc... on a bike that has no built-in provision for those things currently?

Thanks for any suggestions or ideas,

Mark (Windrider1983).