I dont think PSB and REL are exactly what one would call "Match". I dont think there is such a thing as matching subs and speakers, as one can EQ and adjust the cutoff points, the low and high pass filters, phasing, gain and of course placement to compliment the main speakers, or take over where the mains refuse to go as the case may be.
However, since both PSB Speakers, in this case the Image and Imagine series and the REL subs give a fairly flat frequency response, the integration of the sub is quite easy, as compared to a sub that peaks and dips radically at certain frequencies (e.g. most comercial subs).
I have integrated my B6, c5, and B4 with a PB12 nsd with relative ease, however that is for HT purposes only. I prefer the speaker (B6) running full range as it is for pure music, albeit of course within the speakers limits, and the room I have is moderately treated (Absorbers, diffusers, bass traps, carpet) and it never ceases to put a smile on my face.
Cheers
Congrats sa mga kumuha ng REL! thats one awesome sub!!!