Best €2500 sub purely for music?

I recently was lucky enough to try a demo between a two rel 9tx and one s510, and I though the s510 was vastly superior. My only hesitation for being one was that the EU pricing of rels are kinda steep, and maybe im not someone best suited to use them? To explain, I use a minidsp shd preamp to control my entire system. With that I always use a high-pass filter with a extremely sharp roll off of -48db. Anything above 60hz is given to the speakers. I found this to sound night and day better than trying to cross any speaker with their natural cutoff. This is antithetical to how rel designs their subs. Lastly, it only has phase adjustments of 0 and 180. Its for these reasons why im asking you if there are any alternatives to the s510 you recommend between €2k and €3k IN EUROPE (so no svs or rhythmic or any other US brand of any sort) that might be more appropriate for a purely hifi application?

My speakers are German physiks hrs-130's. They're omnidirectional, but what is important here is they a sealed design that is extremely precise and fast, but its not enough SPL for synthetic music. The lesser rel's arnt as fast as it, so I ask for something equivalent to the s series. I only want one, and my room is 30m^2. I will be using the full Dirac calibration of the shd to integrate it, so subs with on-board dsp is completely irrelevant, and I'd rather not spend on a feature that's useless to me. What other options are available here?