Martin Logan 13A's with Rel subs? A match?

james633 yes they do and it works well. The speakers are exceptional.

But that won't prevent me to contemplate building up my system.

I'm still on the fence regarding subs. They might muddy up the sound or take it to another level.  That's the gamble. And an expensive gamble.

I would guess they would make it worse. Adding an active or passive highpass and using a really good sub would do the trick. Honestly that might not be rel. I would look at large subs (15” or more). With as low as your speakes go you will really need to highpass to avoid overlap. Then you need dynamic subs (big) to surpass what you have. Anyway, just my opinion as someone who has been using subs for 15+ years in my two channel. 

Just a thought....

It's voice coil is bigger than most woofers.   2 X 10,000 watt amps included