If you go this route, the speakers will be crossed over at 80Hz (that particular portion of the SMS-1's bass management is a fixed analog crossover at 80Hz, so there's no way to adjust that). You could adjust the low-pass crossover for the sub, which is handled in the digital domain and offers very fine control of both slope and crossover point. For comparison, the RR2150 offers bass management with a 60Hz, 80Hz, or 100Hz crossover point. What speakers would you be using?