Charlie,
I believe your goal is pointless.

Do all the testing you like. It's a total waste of time. You act like you want to get very technical about finding out exactly what the output differences are in high end digital amps compared to middle of the road solid state.

1) Clearly the tests that would need to be done to determine exactly how and in what way a higher end amp sounds better than a lower quality amp don't exist.

2) Despite your seemingly technichal leanings, you miss the most obvious point.... The point I've stated over and over again in one way or another...

You don't listen to bench tests.

You listen to specific cd players preamps, dacs, etc... and the only real POINT of a high end piece of electronics is to sound better to your ears.

The test is -Step One... GET one of these digital amps. You'll need to do this to do any of your silly ancillary bench tests anyway.
You've yet to do step one, so don't tell anyone 'not to peter out on you'. That's just goofy.

Step Two - Replace your 1050 with a preamp. You mentioned a few you have. I'm not familar with their model numbers to make any comment on their transparency, but it should be better than using the rec. as a preamp/dac.

Then get a good CD player or DAC/transport combo, and since you didn't really describe what your DIY speakers are, I don't know if you'll need a sub or not.

You didn't say if you speakers are a 3-way w/ a dedicated bass woofer or if they're a 2-way design or what?
Just taking a guess that they're an M-T-M design w/ dual 6 1/2" aerogel woofers? If so you'd need a sub for true flat 20-20kHz output.

BTW -have you ever used one of your solid state amps w/ the pre/outs in the 1050?
You should probably get at least some improvement in you main speaker's sound quality by doing just that.
If you can't hear any diff. I think you might have a problem with your ears.

Enough is enough now Charlie. Any more talk here is pointless!

Go get an amp if your want to hear the diff. -or don't if you don't want to.
But you'll get no more 'handholding' from me trying to explain to you the most basic elements of an audio system or the POINT of listening to more realistic music for music's sake.

Perhaps you just should go listen to a lovely sine wave at your bench system, pretend you can't get better sound reproduction than that, and grin your life away.