You could wire the CV-out for accent control. It will not trigger when playing a note with velocity set to 127 (like the accent). Instead you should get a smooth volume control via a separate note on+velocity, or controller.
Yes, CV OUT control of Accent works and gives velocity control over Accent amount. However in my case I found there was a lot of cross triggering of Handclap and Rimshot with Accent triggering, so I moved the connection to the other side of R290 (10k resistor) where it joins the base of Q41. I added, from the CV OUT wire, going towards the connection, a 1.5 k resistor, then the 39nF capacitor, then a 10 k resistor. This cured the cross triggering. At this point in the circuit (the base of Q41) the quiescent state is at positive 5 volts, so you have to set the CV out at 5 volts, going negative towards 0 volts with a trigger, and the amplitude controlled by midi velocity. This gives you fully variable Accent, (although the practical usable range is really in the upper third of values) with the total Accent volume still controlled by the front panel pot.
Regarding the Low Tom, I moved it back to the original position, because once the polarity had been changed, either position gave the necessary rumble at higher velocities.
Regarding the Clave: for some reason when messing around with this, I started getting cross-triggering with the Handclap and Rimshot, when connecting to the point I suggested. Not sure what changed because it worked beautifully for a couple of days!! Anyway, I disconnected the internal trigger line for the clave (it’s not programmable and is only used in two presets) and sure enough, that fixed the cross-triggering…. but, the sound changed back to that thin click I was trying to avoid. It turns out that for the Clave to sound properly, there needs to be positive 5 volts on the other side of that input capacitor (C56 27nF). As a quick fix I connected a jumper wire from there to a source of 5 volts on the board, and the sweet clave sound came back!
(I probably should have experimented with a few passive components as I did with the Accent to find a more elegant solution).