What do you see as the downside of tubes?

Jafox, the advantage you hear with Aria may owe more to TX2575 resistors than to tube vs. SS paradigm. Lately to get a better grip on the tube vs. SS debate I've been all out modifying a SS ARC PH-2 in parallel with an Atma-Sphere MP-1 phono section. The usual assumptions about SS being flat, sterile, and lacking tonality relative to tubes does not apply once one replaces the red rectangular Wima MKP caps often used in ARC and many other SS gears. TX2575 resistors as used in Aria are peerless and found in no other commercial gears AFAIK. This story is unfinished until I've put 20-30 of them in SS ARC, but so far these highly modified tube & SS phono sections are pretty close.

Jafox, from your comments and thorough review of Aria and Counterpoint, it would appear that these products owe their distinction primarily to tube power supplies. The flexibility of Aria in accommodating extensive rolling of tube families may also be a factor. Plitron and Dynamicap may be ruled out, as these are fairly common in high-end applications, and Dynamicap IMO is surpassed by several other types, particularly teflon. On the fourth hand, there is nothing like TX2575, which has proven superiority in disparate modded components in my system(e.g. BAT VK75SE, Merlin BBAM, Atma MP-1.)

On the point of rolling the Aria line section (particularly in view of poor results obtained with 6H30) I'm curious whether in addition to the switch between filament voltages, Aria obtains the optimal operating points across so many tube types. In phono section of my modded Atma MP-1, I've been back and forth between 12AT7, 12AV7, and ECC99. Each change requires fairly extensive R swaps for optimal operating point. Of these three tubes ECC99 sounds best-- which appears to have been an also-ran in Aria. So while I respect the versatility of tube rolling, I am cautious about pronoucing the superiority of any particular tube independent of circuit, and question whether a single preamp can do justice to so many tube types.

I'll add that the modded MP-1(which like Aria has the virtue of simplicity) includes replacement of 12AT7s with matched bipolar transistors in first gain stage of phono section(an Allen Wright idea planted in MP-1 by lewm.) This was a clear step up both sonically and in terms of gain. The latest factory iteration of MP-1 adds better CCS regulation to improve 12AT7 performance, so the question remains open from this experiment regarding relative superiority of tube and hybrid in phono. (My PH-2 rebuild will press the point further into FET. BTW, I also had a long run with BAT P10. The modded ARC PH-2 is the keeper.)

Perhaps the discussion boils down to tube vs. SS power supplies. On this point I can offer little other than to add that in my schema, the latest high-voltage silicon carbide zero recovery Schottky rectifiers improve significantly upon soft recovery discrete Hexfreds(or worse, 4-pin bridges) used in SS power supplies in most top gears. Some designers will argue that a tube power supply cannot equal the dynamics and energy of SS. Schottkys also raise the bar in terms of tube-like refinement. So the jury may be out on that one as well.