I just wonder if installing softer shocks and springs - especially if they are progressive rate springs - would make the situation worse. We don't have that much suspension travel. Progressive springs like the stock and the OME 912 & 913 allow you to blow through too much stroke initially and then you've only got a few inches of travel at the firm rate before you hit the bump stops. Trimming the bump stops will give you a little more travel - but then there's less cushion effect when you do hit them.
I don't know what the rates are for the stock springs but according the Rickshaw thread Tom posted the OMEs are 180 lb/in rising to 300 lb/in. Have you ever considered trying some straight rate springs in the 240 lb/inch range? The ride would be firmer but there would be less of that harsh "slamming."
I don't mind the firm ride of the VX but I hate the slamming that results from bottoming out the suspension. I can always tell when my shocks are getting soft and need nitrogen. There's a fairly big set of braking bumps at a stoplight on my way to work. I've hit them at the same speed four or five days a week for years. (gotta love coordinated lights!) Normally the VX handles them with aplomb - very compliant - firm yet not harsh. But when the shocks get too soft, the suspension blows through the stroke, bottoms out and it's a slamfest. I add N2 to firm things back up and all is well with the VX and my weak old back.
Sometimes more firm = less harsh.