what I found is that analog stereo pots don't track well from left to right (esp. at lower volume levels) and also the high freq. response 'merges' (crosstalk) as the freq goes up. its very measurable even with a $100 pc sound card. but once you remove the cheap analog pot and put dual mono attenuators in, crosstalk is highly improved and you get essentially identical tracking if you use 1% resistors (don't really need .1%).
the weak spot is usually (imho) the preamp section. if you disable that in your vintage gear (or bypass/jumper around it) and use an outboard preamp or attenuator, you get a combo that makes the best of both.
for amp sections, I'm using 'chip-amps' that cost about $15/channel to build and they give about 50w/channel. very good cost/perf ratio. good for bi- and tri-amping 