Subwoofer with Thiel 2.4s?

Used RELs are a often a steal, and it mystifies me why anyone wouldn't be able to dial them in to fit with most speakers. Level (the most important knob IMO), frequency point, phase, etc., should allow for just about anybody's taste for bass needs. I have heard that if you have bass heavy main speakers you can risk a wallow in some mud, but in that case just remember the level knob, or move the damn thing around...my older, bought used ($200!) Q150e is astonishing...I stand astonished.

Some of these details are in a couple amp threads that I initiated as I worked to build this system, but my real issue is that I am currently driving the 2.4s with a Pass Labs INT-30A. This combination, while sounding drop dead gorgeous with the right material falls flat on some more complicated stuff (e.g., rap, dance, & movies). I've tried another higher power amplifier (a 400 W Mac 402). This amp sounds great and solved the bass problem, but doesn't image quite as well as the Pass (or reveal as many recording details). I'm also considering a Pass X-250.5, but am still concerned that I'm going to end up missing what the XA amp gives me. It's just so good at imaging (which is the most important sound quality for me) and sounds so natural and grain free that I really don't want to lose it. I know the sub route is a cheating solution, but I'm on a budget and was just hoping that a little augmentation may let me fill in the low end without losing all of the positive qualities of the Pass XA series.

Thanks for the thoughts.

I'm in agreement with Newbee, I prefer subs in pairs rather than in mono.

The SS2s do sound amazingly well integrated with my old Thiel CS2.4SE and the Thiel CS3.7s.

I have heard the JL Audio and it just seemed a tad slower off pace than the SS2s in the same dealer showroom

The SS2s don't call attention to themselves and just make the 2.4 and 3.7s into much larger speakers.

I think one reviewer said not to look at it as an expensive subwoofer but making a Grade A speaker (band limited) into a Grade A speaker (with full bandwidth) :)

Thiel has a new Sub out for this year, which is a little smaller in size than the previous model. I am looking to get that for my SCS4's.