TTS-1 drum note velocity problem

I have been using Cakewalk with external synths since DOS days, but just started using the TTS-1. Sequences I have been using for years sound good on the TTS-1, although most require a little rebalancing between instruments.
 
I'm having a problem with drums - the TTS-1 seems to ignore velocity settings for individual drum notes. Whether I want to reduce all kicks or cymbal crashes relative to other drums, or change individual velocities (a soft kick just before a louder one, for example), all of the sounds seem to follow the balance in the drum set, ignoring my midi velocities. The same sequences behave as expected when played through my external synth or the MS wavetable synth.

My apologies if this has been addressed elsewhere. I haven't used forums much, and a quick look around didn't turn up anything that seemed relevant.