Hi Mudge
Have you had the chance to hear any of the bigger REL subs? I can see your point if you were looking at adding a REL Strata to a pair of 6 or 7ks, but realistically, you'd be looking at the REL Stadium and upwards. I'm using a Stentor III, and it works very well indeed (in an otherwise all digital Meridian system).
To answer one of the earlier posts, the published spec of the D2500 seems to vary depending on what page of Meridian's site you find it, but the hard copy brochures currently state 20Hz-160Hz, and that has been the published figure in print for the past four or five years.
Regards
George