Atma-Sphere in CO?

I own both the Franks and the Atma-sphere M-60's, and use the amps to drive Coincident Super Victory II's and Coincident Triumph Extreme II's.  Let me say at the outset that I love both amps and have no desire to sell either.  Several years ago, I did a long and careful audition of the Franks driving PRE's, so I have a good feel for the combo you have. I suspect this will be a tough choice for you, and the best option is to do a long evaluation in your room with your ancillaries with both amps side by side.  You already know the virtues of the Franks.  What I can tell you is that the M-60's equal the Franks in many respects, but the amps do diverge on some attributes.  As you know, and as Ralph has pointed out on numerous occasions, 300B amps are at their best when driven gently.  Distortion rises rapidly above 1-2 W output.  For me, that is an issue.  I listen to a lot of orchestral music, so rising distortion became an issue driving the 92.5 dB efficient SVII's.  Rising distortion will never trouble you with your PREs driven by M-60's.   If you mostly listen to small scale works, with peak volumes at or below 90dB in a smallish room, rising distortion may not be a significant issue.  You will find the M-60's lack some of the wonderful sonority of the Franks, but not much, provided that you select good driver tubes to replace the awful (in my opinion) Chinese 6SN7s that are stock.  I really favor the NOS RCA 6SN7s, myself.  For me those tubes bring some of the 300B virtues to the M-60's.  The less expensive 1960's vintage 6SN7GB tubes are fine.  It is not necessary to use the uber expensive 40's and 50's vintage tubes.  Also relevant is that I ordered my M-60s with the V-cap upgrade and the power supply upgrade.   I do hope you are able to arrange a long audition with the M-60's having an appropriate driver tube compliment, and I will be very interested in your conclusions. 

@brownsfan Thanks so much for the information... super useful.  Will probably also demo a Pass XA-25, that's at least easy to get in the room for a 30 day demo and I'd love to be able to just leave the stereo on all day without concern for tube life.

@cal3713 ,  I've also thought about giving Pass or First Watt at try, and almost went that way before I bought the M-60's.  The problem is that when I like something, I don't want to give it up.  That is why I ended up keeping the Franks.  If I brought in an XA 30.8, I'd probably end up with 3 amps.  For what its worth, you can leave the M-60's in standby mode if you like.  There is no B+ voltage in standby, so I'm not sure that compromises tube life, and the amps don't generate much heat in standby.  Ralph can give you a better answer on that stuff. 

I'd love to be able to just leave the stereo on all day without concern for tube life.

If the amps are on a moderate load (and most Coincidents are) then the tube life is really really long. I leave my amps on all day and most of the night without worries, although I do put them in standby if I step out for dinner or the like.