I just bought a Nuforce P-8 preamp to match my Nuforce 8.5 amps.  My previous preamp had developed a hum.  I don't know if you would call this a level, but this has got me thinking.  The P-8 and 8.5's together give a sound that makes me question mixing and matching preamps and amps.  I can play whole cd's now.  When we mix and match, don't we also just listen to a cut from one, and a cut from another cd(or lp)?  Shouldn't we ask, "can you play the whole cd and does it all sound good?".