Amp-less Velodyne F-1500 Question

I picked up a Velodyne F-1500 sub in great condition but no amp. My question is how much did (does) the original Velo amp with it's servo-loop feature matter in the performance of the driver and it's box.

I have the sub hooked up to a Parts Express 150 watt plate amp mated with a pair of Altec Model 9's. I've varied the crossover from 80hz down to around 50. Performance is so-so. Way mushier than my very tight sounding Altec 411-8a in an 8 cubic ft sealed box using the same amp. Never heard a Velodyne nor a servo-sub so I've no basis to compare. I would love to get this Velodyne up and running without having to find an orphaned Velodyne F-1500 amp...Any info or suggestions are greatly appreciated.

I'm new to the forum and this is my first post.