Adcom GTP-500 vs GTP-500II

Any opinions? I currently have a GTP-400 mated to a GFA-535 in my 'legacy' system (bought new in late-80's) looking for a replacement for the 400 if source selector issues can't be resolved.. so, any significant differences between the first-generation 500 and the mk2 ? thanks in advance.
Thank you to bchasteen for his/her response about the online manuals, I should mention that I had already looked those over and there appear to be some differences in specifications (btw the mk2 manual is much more detailed in this respect) but rather than getting bogged down in numbers,I was really looking for any opinions from audiophiles who may have experience with both and could relate their opinions on the sonic differnces, if any, between the two... btw, the GTP-400 compares favorably to both, lacking only the tone control bypass circuit and has only the non-filtered outputs which I would be using anyway w/ my Adcom amp. Thanks.