Need suggestions for subwoofer suitable amp replacement

It is finally time for me to find a substitute for my ailing, ancient NAD 3155 integrated amp. However, I have a particular need: I have a custom sub that takes a pre-out feed from the amp, but when the sub was made, the guys who built it did something to my amp. Ordinarily the pre-out on the NAD is for bridging, but they made some sort of internal connection that makes it available for the sub while the amp section continues to run in stereo, non-bridged mode.
My question is, 1) what amps would you suggest as a contemporary upgrade (for say 1k or less), and 2) will I have any problems finding integrated amps that can provide a pre-out line feed to the sub without defeating their own amp section? Any suggestions would be very much appreciated. With the sub I have a pair of Spica TC-50s, modified and bi-wired, and an Arcam CD72.

Thanks! I'm very interested by the NAD's second set of pre-outs. I'm also checking out the Arcam 65.

Arcam makes a wonderful product but it's more expensive.