Responses from gareents

Maximum Upgrade Potential
I believe that improvements over the last 20+ years, and still ongoing today, differ depending on the type of amplifier. Solid state has changed significantly, as pointed out by @ghdprentice using Pass as an example. However, changes in SET amplif... 
Pass Labs XP32 or XP22?
I also use an ARC preamp (REF 3) with Pass amp (XA30.8). Tried others but this is best combination.    
What speakers work with low wattage class A amps
Spatial Audio. Open baffle, 90+ dB sensitivity. I drive Spatial X5's with a Pass XA30.8 very easily.  
Considering moving to separates with a tube preamp-appreciate recommendations
I would second going to an ARC preamp. I replaced a BHK, and a CJ ET5SE, with a REF3. ARC is superior by far!     -G  
New take on CD vs Vinyl vs CD
I think your results are due in a large part to the level of equipment being used. No offense, but the CDR and CD players being used are not particularly high end. You did not even mention what turntable was used, but an Ortofon Blue is definitely... 
Two powered subs with bookshelf speakers or two floor-standing speakers?
I had a number of very good bookshelf speakers (B&W 805D, Harbeth 30.2) and subwoofers (REL, SVS) in different rooms. Sound was very good but not even close to floor standers I now use (Wilson, Spatial Audio). As others stated above, integrati... 
Early Impressions of Lab12 Integre4
No surprise that you preferred Lab12 to PrimaLuna. I did a direct in-home comparison of five different integrated amps, of which PrimaLuna was one. PrimaLuna was least capable, dark mushy sound with poor dynamics. In spite of what uncle Kevin keep... 
What Gear Has Disappointed You?
Rogue Pharaoh integrated amp - bright and thin Harbeth 30.2 speakers - so very average    
ARC REF 3 vs Modwright 36.5 DM
Thanks, I greatly appreciate all of the thoughtful responses. BTW, yes I am using both balanced and single ended connections. I would agree that SE connections are a little warmer, but also lose detail. Thanks for the Backert Labs and Herron rec... 
Luxman Knockoffs or Counterfeits?
I have purchased audio equipment (SME tonearm, turntable parts) from Japan via Ebay. No problem and great result. I always look at the Ebay ratings of the supplier and find this to be a very good indicator in terms of the number of raters and the ... 
Transients hurting my ears on hifi solid state amps
I had a Rogue Sphinx and completely agree it was one of the brightest amps I have ever heard. Sold it off after a few months. As others have mentioned, moving to a good SS class A amp was the solution that worked for me. I now have both a Pass 30... 
Why not?
Raven Audio includes their well made power cords with their amps.  
Looking for good recordings of female vocals I have not yet tried...
All very good suggestions above. But for an amazing voice performer that no one has mentioned, or probably heard, check out Chris Webster. Locally famous in Northern California. Quboz has only two of her albums, but a good start! -G  
3k Phono preamp upgrade options (JC3+, XP-17, etc)
@riskymilk  Regarding differences between Pass XP17, PS Audio Steller, and Parasound JC3+, they are closer than different. The Steller is dead quiet, more than the JC3+, a little more resolution than the JC3+, but maybe not quite as dynamic. Bot... 
3k Phono preamp upgrade options (JC3+, XP-17, etc)
@riskymilk - I own the Pass XP-17, JC3+, and PS Audio Steller phono preamps. All are extremely good. The Pass XP-17 is the best.        -GAR