Rauliruegas:
As a matter of fact, I HAVE been contemplating two subs with a higher crossover point, but haven't worked out the logistics of where to put the second sub. Plus, setting the subwoofer crossover to a higher frequency would seem to mandate the use of high quality capicitors to block the lower end output of the mains from the same point on downward, both to avoid midbass boominess from frequency response overlap and to free up the midbass driver of the mains (which in my case are the Intuitive Design Summits) to function as more of a pure midrange driver. This would likely obviate the "Doppler issues" that Dale Pitcher had referred to, but which I honestly haven't been able to hear. Nevertheless, maybe their already outstanding midrange could be made even better by doing so.
Anyway, from a practical (and financial) standpoint, for now at least, the single Rel in the corner works surprisingly well (for me). I did, however, purchase the Summits with the possibility of upgrading to two subwoofers in mind. Part of the pleasant surprise with the Summits was that, for now at least, that doesn't seem like a pressing need, even though they're two ways that go quite low.
Bill