Best Class A amp with SLAM

You should add to your audition list the Electrocompaniet AW series monoblocks: AW180, AW400 and AW600 (Nemo)

Smooth sound and can handle loads down to .5 ohms.

I also own the Pass XA.5 series, and although I love mine, it seems that these amps are a bit reticent in the bass/slam department. I've read that enough times from enough different people that I'm pretty comfortable attributing the issue to the amps.

Most slam?

Probably the biggest, heaviest, highest wattage, power gulping, least green, most expensive one out there, whatever that is?

I could have used a pair like that with my large OHM 5 speakers.

But not practical for me (or most) so I tried Class D and have not looked back.

Another vote to Symphonic Line Kraft 300. Fast, sweet and big sound with unlimited dynamics.

I owned many Pass Labs poweramps. If you choose for the XA or X series ( Always .5 ofcourse)you both cannot go wrong. The XA are a little more musical and the stage is maybe more 3D. But the drive and speed of the X series is better. Also the high's sound more open at higher volumes. My next will be X600.5 or maybe the XA160.5. Pass Labs gives a deep and wide stage. And is one of the best in focussing on the real sound of instruments. But you need the right cables to get the very small and direct individual focus instruments and voices give in real. Many make the same fault in this part. Do not use MIT or Shunyata cables with Pass. because you will not get the intimate sound you need. When you compare Audioquest with these two brands on Pass Labs you understand why the other two make the proportion of instruments and voice too big. You Always need to understand the properties of an amp before you choose the cables. Because they have there own properties as well.