I don't believe that the 970 allows PLIIx processing of the multichannel analog input even in the digital bass management setting. It does add an A-D-A conversion, but what sonic impact it has I don't know (the 990's 7.1 Direct input is still extremely transparent even with that conversion, but it's also got beefier DAC's than the 970). The "bypass" or "HPF/LPF" settings would be the safest course, although you could easily do a little comparison listening to find which you prefer.