In the last few weeks, i've fired my tube integrated, gone to Outlaw Audio's RR2150. This stereo receiver has a sub out and internal low pass selectable at either 60, 80, 100hz or bypass (so you have the option of using your sub's crossovers).
I didn't add a sub until this weekend, stole the Def Tech PF 15 from the home theater system. I feel like a heratic but this is much, much, much, better!!
The sub doesn't work very hard normally, but it does contribute. I don't consider the PF 15 to be very high end, adequate at best. It will need to be upgraded to really "fit" with the khorns if you will. Probably will look at a 10" or 12" sub in the future.