I’ve used numerous good quality class AB and class D amps on Magnepans and have noticed a difference to the bass reproduced between the two but have not read much from others on these differences that I clearly perceive. IOW, it could be just me.
I’ve achieved good results with both but perceive the bass from the class D amps I’ve used as being more solid, powerful and dynamic. In fact, I distinctly recall thinking the bass reproduced through my first class D amp, a Class D Audio SDS-440-CS stereo unit, was noticeably the best bass I’d ever heard my Magnepan 2.7QR speakers produce since I owned them.
After careful comparison and contemplation, however, I came to the conclusion that the bass was a bit exaggerated with the class D and seemed to truncate the decay times on bass notes, most likely due to its Damping Factor being rated at a few thousand as opposed to my class AB amps being rated at a few hundred.
I currently believe this ultra high damping factor on both channels resulted in firmer control of the starting and stopping of the rather large 623 sq. in. planar-magnetic bass sections on each of the 2.7QRs, which tended to exaggerate the leading edges of the bass notes and truncate the decay times.
While I admittedly enjoyed this overall bass overemphasis on my system in general, I ultimately realized it wasn’t as accurate or natural as I convinced myself I should strive for. So I purchased an Audio Kinesis Swarm 4-sub distributed bass array (DBA) system powered by a 1K watt class AB amp/control unit. In combination with my then 2.7QR and current 3.7i Magnepans, I’ve perceived these systems bass performance as being more accurately and naturally powerful and dynamic while also providing more accurate and natural decay times.
While I don’t know for certain and have no experience with any Purifi amps yet, I believe class D amps in general share these very high damping factors and, therefore, the bass qualities I described. Ymmv, of course, but I thought my experiences may be of some use to you since you’re likely to have similar perceptions of the bass performance differences as I do. I also tend to doubt you’ll be able to perceive any significant bass performance differences based on amperage capacity and current delivery.
Tim