I have M50's connected to IRD monoblocks to a Morrisson ELAD preamp with source from Sony sacd/dvd/cd player. My problem is, how can I connect my subwoofer to this set-up. My subwoofer at this time is hooked up with my yamaha receiver to my HT set-up.

If your preamp doesn't have a LFE output, I think you'll need to use the speaker inputs on the sub.

Here's a link that explains it.