"Double bass" refers to the scenario where you have bass management transferring information to the subwoofer output from other channels while leaving that information intact on those channels. As Kevin pointed out, both the Outlaw 950 and Rotel 1066 include a low-pass filter on the 5.1 analog input that passes material below 80Hz from the five full-range channels to the sub. The 1066 leaves those full-range signals unchanged, however, so that the "bass" information is output twice. The 950 has a switch to enable or disable a high-pass filter for the five full-range channels (the analog bass management that David refers to). If you are using the ICBM, you should not be encountering double bass (I don't know of any scenario where you could produce this with the ICBM).

With the 950, you would probably not need the ICBM between pre-amp and amp -- not useless, but basically redundant. The digital bass management on the 950 provides much the same functionality as the ICBM (separate crossovers for center, mains, and surrounds, with similar or identical crossover point options to choose from).

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