I have to say, I can not see the point of filtering a regenerated AC. If you need to, surely the regenerator is not doing its job. I changed from a competent filter, the Kemp to the APS 1050 with very clear benefits in noise floor, dynamics.
If I was going to add to the APS, it would be with the Quantam Q2 or 4. I am not sure what it does, but it certainly does it. I heard HiFi +'s demonstration of ancillaries at the Heathrow show a few weeks ago, I believe they did a similar one at RMAF. The Quantum was , to me the clear winner in sound improvement as the ancillarires were built up. Does anyone who attended RMAF agree? The same demo, but using different box's