One last question for now: To find optimal positioning for my front speakers should I just run REW with each speaker alone and find the optimal position then do the other then do the sub and finally see how they integrate together? Also, what frequency range should I focus on?
Personally, I try to find a good location for the mains by listening in two-channel stereo mode. I try to get good imaging and soundstaging going, etc. I've never tried to place main speakers based on REW measurements. And I've tried a lot of stuff with REW.
Low bass (let's say less than 80 Hz or 100 Hz) is going to be powerful enough to excite the room modes themselves; the higher frequencies generated by your mains just don't interact as much with the room as the sub does. Therefore, locating the sub in different places around the room will have a bigger impact on bass frequency response than will main placement; probably by a lot (again, no experience with intentionally moving around mains to deal with bass/room mode issues). On the other hand, if your speakers are bass-capable, they too, will interact with the room, and their placement in the room will cause frequency response to change.
All that said, I'd focus strictly on the sub. Engage the crossover as you will use it in practice (50 Hz, 80 Hz, whatever you want it to be). Turn off all other speakers. Phase will not matter, because it's only applicable when there are other speakers. Sweep from REW's minimum (which I believe is not changeable right now), and end the sweep at 200 Hz. I think you said your crossover point was 80 Hz, so sweeping to 200 Hz will be fine. Post your graphs from 45 to 105 dB on the vertical (Y) axis and 15 to 200 Hz on the horizontal (X). If you're going to do a series of measurements, plot them on the same set of axes (you've already been doing that).
Once you get your sub response the way you want (either through placement, treatments or EQ), turn the mains back on. You may have an interaction at the crossover point -- play with phase if you can. You may notice peaks and dips, and you may not be able to do anything about them. Of course, you can try moving mains around.
Geez, I just wrote this whole thing thinking that you are trying to fix your sub frequency response. You've ordered an SMS-1 but it's not there yet... Duh! Anyway, it still all applies, from my point of view. Get the sub right first, and then integrate the mains, etc.
You'll have even more fun when the SMS-1 gets there!
Good luck!
