I have used a couple of different passive volume controls... they are theoretically a great solution, but they need to be carefully impedance matched to your source and load or they will very markedly change your frequency response. I have never been able to make one work for me as well as a good active line stage. Even when the response wasn't rolled off there was a lack of punch and immediacy... in your system you seem to have gotten it to work for you. Changing your crossover or other gear will change this delicate balance.
As for DEQX... it is fussy but powerful. I think it is a fantastic tool for designing and playing around in the DIY world, but short of using their digital in and out model with outboard A to D and DAC it isn't as good as a better all analog system. Their new HD versions are better (anecdotally, I have no personal experience) but there are other DEQX issues... for the right person I'd recommend them, but in general I'd go in that direction with caution.
Widget