I know this is very simple, but DID YOU CALL KEF??? THAT's the place to start. They will know their speakers better than anyone else.
Your biggest problem might be your cabling - Nordost has never been known for strong bass. Adding VD cables is also a very good suggestion, before you even CONSIDER modifying those speakers.
The 501's should drive the KEF's fine - they are much more efficient than the B&W's referred to by an above poster. It could also be your room at fault, but in your case I'd say there's an even better chance your bass choke-point is the cabling.
You can demo some different cabling from The Cable Company and they can give you some suggestions as to what might work better for your application. They are good to work with and usually very helpful. That way you can try different cables without paying much out-of-pocket and your "rental money" counts towards whatever you purchase.
Good luck - this sounds very fixable.
Your biggest problem might be your cabling - Nordost has never been known for strong bass. Adding VD cables is also a very good suggestion, before you even CONSIDER modifying those speakers.
The 501's should drive the KEF's fine - they are much more efficient than the B&W's referred to by an above poster. It could also be your room at fault, but in your case I'd say there's an even better chance your bass choke-point is the cabling.
You can demo some different cabling from The Cable Company and they can give you some suggestions as to what might work better for your application. They are good to work with and usually very helpful. That way you can try different cables without paying much out-of-pocket and your "rental money" counts towards whatever you purchase.
Good luck - this sounds very fixable.