amp clipping or low freq causing pumping speakers

My cd source plays back fine at loud volumes with modest amplfication. My analog MC setup needs much more volume and until I switched out my premap from a Dodd battery powered to my present highly resolving
Doshi Alaap I had little to no pumping / displacement in my bass drivers (Salk HT3's).

Now they noticably vibrate in and out with some breakup distortion. Not as much with jazz but more so with dense rock music. Unfortunately quieter passages are too far in the background when played requiring higher volumes (perhaps I need more preamp gain). CD's with their higher compression sound fabulous on the Doshi and with less volume required

I have seen this once before when at an audiophile meeting a friend brought over an Infinity pre that went down to subsonic frequencies and my speakers were vibrating

my dilema is I need to turn my turntable up louder than my cds(which sound great and don't clip).

Could it be the added dynamic range and more low end of analog sending the speaker into viration mode

Or is the amp clipping not being able to reproduce the load sent to it?

I have a Moscode 401 HR amp, I have a higher powered BAT VK600 with a friend 1200 miles away.

thanks

Tom