Dan, I didn't see where the DA4ES has an assignable amp channel which can be used to power a passive sub. The Kenwood 6070 has such a 6th channel, but if it's used to power a sub, then the 6th channel isn't available for the back surround. If you'd like to go in that direction though, it's likely that you already have an amp to power, say, a SVS 25-31CS. Your present receiver or some old receiver that has 100 watts or so per channel would be fine to power it. The sub out from whatever new receiver you get would go to any line-level input(e.g. CD)on the old receiver and then a speaker wire from the corresponding speaker terminals on the old receiver would go to the terminals on the passive sub.
