Perhaps an Involve decode and a S&IC or QSD-1 decode of the same material for comparison?
Although It might be simpler to simply listen to the unit bypassed perhaps as double stereo and then listen to the Involve output. The change in sound quality (disregarding directional effects) should be obvious, or at least noticeable.
I remember someone complaining about weak bass from the Involve decoder. I've noticed that with several vintage decoders as well. Many decoders use much to low a value of output capacitor. Units may test flat into a normal load (whatever that is) but into a lowish impedance bass response will drop. People forget or are unaware that if each piece of equipment is rated down to say 20Hz, that usually means -3dB at 20 Hz, so the poles compound causing even more bass loss overall. The Composer used 10µF for all outputs and on the input, pushing the low frequency drop off away down. I never notice any reduction of bass frequencies. I replaced the output capacitors in the QSD-1 changing from 1µF up to the same value used in the S&IC (10µF). The sound (bass) quality improved greatly, tonally it's now about the same as the Composer.
I never understood why most op-amp based circuits (operated from bipolar power supplies) almost always include unneeded coupling capacitors, they are best left out! I still remember a brief while when DC coupled audio circuitry was a big thing!
