From all the wisdom I've read on Audiogon and many other sources, buy another sub, and work on placement. There is lots of advice out there on placement. I don't think you'll here a big difference in the mids and highs m30 vs the M20. The big difference would be the bass between the two. With the subs you are biamping and your Levinson 383 should sound its best. I'll bet it will be killer. You could also check into buying the model above the Rel Sub you have too.
Another option would be to pick up Revels B-15 sub.It sounds great with your speakers as I've heard it with them. It has great setup directions with a 15 inch woofer.
As I'm thinking that might be the best way to go.
Steven
Another option would be to pick up Revels B-15 sub.It sounds great with your speakers as I've heard it with them. It has great setup directions with a 15 inch woofer.
As I'm thinking that might be the best way to go.
Steven