When you turn the sub on, the LFE channel no longer goes to the mains. That should be the only real change. There will be a need to recalibrate the system to get the sub set to the right level, which is probably the first place to look.

Another thought: unless you are using 7 Stereo, the side and rear surrounds will rarely get a lot of bass, so hooking a sub to them may not be a very great use of that sub. It may be more effective (and simpler on your speaker wiring) to use a splitter from the 950's subwoofer output to run line-level connections to both the PSW10 and the Velodyne and then run the side and rear surrounds as "small" with an 80Hz crossover or so. That way both subs would handle the LFE and would pick up the occasional low frequency from the surrounds. Just something to think about...