Atma-Sphere in CO?

Thanks again for all the input folks.  Will be very curious to find out how it shakes out... I pick up the amps tomorrow, so I should know more by the end of the weekend.

I've now gotten a good demo with the M-60 (it came with a nice set of VT-321s, including RCA smoked glass and Ken-Rads). I believe it improved on the Frankensteins in two dimensions: 1) bass definition & quantity, and 2) "cleanliness," the sound was super clean and I could tell there was very little distortion in the signal. Unfortunately, these improvements also came with a cost, in that I lost a degree of realness/naturalness. There was less texture or color to the sound than through the Frankensteins. I wish I could just marry the two amplifiers to get the best of both worlds, but in the end decided that bass was less important than realness, and will be sticking with the Frankensteins.  

At this point I'm starting to lean towards just keeping the Franksteins and dealing with the slightly reduced bass output. I got new cables (constructed from the 16ga Duelund WE replica wire) a couple weeks ago and that has really improved the bass situation as well. Now that they are broken in, the Franksteins do not really sound lean at all. Due to some unfortunate life situations I had been limping along with a combination of old budget MIT cables (that I'd also had to repair myself after a connector broke off) and anti-cables and it is now clear that they were actively preventing me from hearing the bass content the Franks/PRE combination was capable of.

In any case, I am growing more and more impressed with the Frankensteins. They're still in the system despite bringing in both the M-60s and the Lyngdorf TDAI-3400. I may also try the Pass XA-25, but do not really anticipate them beating out the Franks given what I've heard over the past few weeks. I may just decide to invest in getting as much as possible out of the Franks by upgrading power cables and installing Dueland capacitors.

@cal3713 thanks for the update.   I am well aware of the virtues of the Franks, which is why I am keeping them.  If I had to choose between the Franks and the M-60's, I'd probably keep the M-60's, but it would be a though choice.   Your PREs are more efficient than my SVIIs, so I can see how the balance might be tipped towards the Franks in your case. BTW, what tubes are you using in the Franks?
Its funny, I've thought about bringing in a Lyngdorf for my downstairs system, where I have significant room acoustics challenges, and returning the Franks to the upstairs system for use with smaller scale works.  But if I do that, I will not be letting go of the M-60's.
Keep us posted if you bring in the Pass.  I will be surprised if it displaces the Franks, but it would be an interesting experiment. 
I assume you are talking about installing the Duelunds in the Franks.  I haven't done that yet, but you might want to consider the PRE crossovers also.  I recently rebuilt the crossovers of my SVIIs, and the work substantially improved bass articulation among other improvements.  I don't have any actual knowledge of the PRE crossover design, but in Coincident models below the PRE, the design and parts list seems pretty consistent.  My guess is if you look you will find Solen caps and resistors, and they are not all that hard to beat.