My experience concurs with D10’s.
A few years ago, when auditioning amps against my CAT (Convergent Audio Technology) JL3’s, we tried a Pass amp in the 250 watt range. It was a no-go!! And this was with consummate Backplates and PX panels. You said you had NON-PX panels and didn’t mention the Backplates. In any case, with NON-PX panels, the more watts the better – my guess the Pass x350 at a minimum with the x600 Pass probably more like it!
Before acquiring CAT amplification, I used a stereo Mark Levinson 336 amp @350 w/ch. It did just fine with the Soundlabs I owned then — M1 NON-PX panels, NON-Consummate Backplates.
Years ago, upon auditioning Parasound Halo JC1’s and then CAT JL1’s (a crazy underrated 100 w/ch.) against my Levinson 336, the CAT’s won absolutely hands-down — no comparison, no contest!! The Halo JC1’s were comparable to my Levinson. At that time, the cost difference was $10k for the Levinson vs $6k for the Parasound Halo’s. Thus, lacking a lengthy audition comparing both amps, my conclusion was that the Halo’s were a bargain. Because the CAT JL1’s were so damn much better in every area, there was no need to do a lengthy audition of the Parasounds. The CAT’s simply CONTROLLED the Soundlabs to an astonishingly degree when compared to the other 2-solid state amps. Bass was better, drive was better and nothing was diminished as far as resolution and frequency response was concerned. In fact, midrange was comparable to the SET amplification magic for which I had previous experiences — of course that was with other than Soundlabs (grin).
Later, after purchasing the CAT JL1’s (8 output tubes per monoblock) a few years thereafter, I had the opportunity to upgrade to CAT JL3’s (16 output tubes per monoblock).
Primarily Convergent Audio Technology (CAT) is known for their pre-amps. But from my experiences, CAT amps are where the company’s sweet spot really resides. However, because 55-pound transformers are used in the CAT’s, they are 190-pound (each) beasts. This coupled with my ensuing hip and spine problems, plus a sacrificial resistor at each tube socket, prompted me to seek different amplification. Unfortunately when a CAT’s (1 of 32 [CAT JL3] output tubes goes, it generally takes a resistor with it. In that case, one needs to manhandle 190-pounds by flipping the amp on its top, removing dozens of screws and de-soldering / re-soldering a new resistor that acts as a fuse. This was becoming a much too much of a literal PITA for me!!
Thus, I auditioned the Pass Amp previously mentioned, a Mark Levinson in the range of 250 watts and Atma-sphere MA1’s. The Atma-sphere MA-1’s were comparable sonically and in drivability to my CAT JL3’s. And at 36-pounds each and with fuses as opposed to (32) PITA sacrificial resistors, the decision to trade my CAT’s for the MA-1’s was an easy one!!
I should add that during my auditioning of the MA-1’s, the Mark Levinson choked – its protection circuit shut it down. Whether that was because it was fairly new or not, I don’t know. Additionally, the dealer had brought a pair of Rogue amps, but with the Levinson experience, he didn’t even take them out of his van.
The MA1’s drive my M1PX with their consummate Backplates with aplomb. How well they would do with NON-PX panels and NON-Consummate Backplates I don’t know!?! Perhaps someone can chime-in with their experiences of MA1’s and the Soundlab A1’s you specified.
After buying the Atma-sphere MA1’s, I must add that Ralph Karsten is one of the best and kindest manufacturers I have ever had the pleasure of dealing. He responds promptly to emails and does a good job of hand-holding new customers. I had an initial issue with the DC-Offset Adjustment. And Ralph simply advised to switch one tube from one bank of the amp to the other. Surprisingly, this can be done while the amp is operational, with the important proviso that heat-preventative material/gloves be used!! This robustness of hot swapping tubes and with a design of fuses as opposed to hand soldered resistors was a huge boon for me verses my CAT experience. I couldn’t recommend more than I already have the Atma-sphere / Soundlab combination. It just works!! -Mike