If the powered sub works like a REL by allowing a power amp output connection (rare I think), the impedence is something like 100,000 ohms so it presents almost no load to the amp. Otherwise it's a preamp output signal to the sub so the power amp doesn't care, and neither do I (heh). I run a REL from the same posts as the main speaker feeds so it all remains equal, and I use the 4 ohm posts...my speakers are 8 ohm rated but (as many do) they dip lower, and the Jolida's 4 ohm posts seem to sound a little better.
