I have been there, and have just finished my dedicated home theater/listening room and ran into every question you will, so take this advice: bass, bass, bass.
After everything that's been read and researched your treatments can easily be summed up by these statements:
1) Treat ALL corners for bass as this is where it builds up. Most rooms have the same frequency problems in this area so a carte blanche-type absorption will most likely work best. I personally used Auralex LENRDs stacked 4-high to the ceiling (I have 9' foot ceilings), so you would actually have less gap in your 8.5 foot-high room. Other options are available, however: www.realtraps.com I would also recommend checking out these sites: www.recording.org and www.auralex.com
2) once you have a general idea of where speakers will go creat an RFZ area, or a "reflection free zone." Determine first order order reflections by having someone place a mirror at speaker/driver level and have them drag it along the wall while you sit in your listening position. Whenever you can see the speaker from your listening position, treat that area accordingly. I recommend acoustic foam because of its application simplicity; however, some audiophile gurus say foam creates an environment that's 'less' natural. Finding the first order points go for ALL speakers, even if you're only running a 2-channel system.
For home theaters, diffusors on the ceilings and back wall (even for 2-channel systems) increases spaciousness so treat accordingly.
Going to realtraps.com, auralex.com and recording.org will take you EVERYWHERE you need to go. From DIY absorbers/diffusors to real-time, real-world application, the answers are here.
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