While I don't have a schematic of the filters in the Isobar, my assumption would be that the filters are cascaded, with the attenuation of one bank being added to the next.

The sound quality from your 2150 won't be effected by whichever outlet bank you use, but I'd plug it into the bank with the least attenuation of EMI/RFI. This is because the current capability of that bank is likely to be higher because of the simpler filtering (series inductor especially).

One very important thing to note is that most people, most of the time, have very little or no EMI/RFI on their power lines, so there is nothing for the Isobar to filter out. Sometimes people believe that EMI/RFI is an all-present, all-the-time danger which is causing subtle degredation of sound quality, but that is not necessairly so. The primary source of these pollutants is from your own home, and your neighbors who share the pole transformer servicing your homes. Even when it is present, it is usually transient in nature - a buzz which comes and goes for instance. Some interference, such as distortion on the power line, cannot be filtered out by any means short of outright regeneration of the AC power - a very expensive and usually unnecessary option.