Huck,
On the same circuit, OL1 = outlet #1, OL2 = oulet #2, so on and so forth. In order to try your 7 PE's on non-audio circuits, I would not pull those Hubbell duplexes that are already in place, but I would re-orient the wiring on those non-audio circuits to the bottom screws to take full advantages of PE filtering. Count how many outlets there are in each circuit. Pending number of PE's on hand, you will not have to treat each circuit. Find the brighter sounding outlet(s), referring to Alan's guidelines, and start PE treating from there.
For instance, if you need to treat a circuit with 7 outlets: OL1 > OL 2 > ... > OL7, this is how I would place the PE's:
PE > OL2 > OL3 > PE > OL5 > OL6 > PE. You'd have 4 more PE's for other circuits.
Like Alan's said, experimentation is key for PE tuning. PE initial effects can be heard after 20 minutes and 5-7 days for full effects. Change them around until you find the sound most liked. After you're fully satisfied with the sound, you can decide whether to pull the existing Hubbells and put them at the outlets where you install the PE's in order to further enhance the PE effects.