I initially set sub, surrounds, and center channel to match volume of mains from listening position. This did not deliver the expected result, I do not know why, but speculate that it might have something to do with speaker distance having been previously set. At any rate, the desired result from volume matching was better integration of the subwoofer. And when SPL was matched at the listening position, the bass violin appeared to be front and center of vocals from Diana Krall's Love Scenes. Re-addressing SPL matching at each speaker the bass violin fell into place. This was not the expected outcome but it is what worked to get the desired result using my OPPO-205 bass management control. The OPPO allows crossover/distance/trim for each speaker. And, BTW, I think lovinthehd is absolutely right about taking the SLP measurements from the listening position being best; yet, this approach did not get the job done in my case. Again, I think it has something to do with when distance parameters are set, before or after volume matching; but, I am unsure about that and not really interested in it, since my 5.1 music sounds just right.