Room Correction, Acoustic Treatment, Positioning, etc. What are my options

Hi mayor:.
1) The shape of the graph makes me wonder if you are using a calibrated mic. You should double check the the calibration factors are input correctly.
2) I would think your biggest problem is the null at 600hz. Eq cannot fix a dip. Google SBIR calculation and check to see if the null correlates to speaker placement.
3) Matt at AV Nirvana is an expert on reading REW graphs. Occasionally the REW developer (JM) weighs in as well. You could solicit advice there.
4) I think most people go at this slowly checking the effect of incremental rm treatment instead of the Big Bang approach. Good luck. I personally enjoyed the journey.

I agree with mikexxyz.  Are you using a calibrated mic, or a SPL meter?  Is your computer set up properly?  Sometimes you need to turn off the computer mic, otherwise, that is used as the default.  The high frequency roll off is very suspicious.  You might do well to go to the REW forum and ask for guidance on insuring you have REW set up properly..  Assuming all is right on that end and the readings are real, what kind of flooring and walls are present in the room?  A dip at 70 Hz in a room with drywall and plywood sub flooring can be expected.  What kind of decay times are you seeing?  Boomy bass could be due to excessive decay times (above 300-400 milliseconds) below 300 Hz.  Bass traps can really help with this.  I have a combination of GIF and Realtraps in my room, and about 2K worth of traps made a world of difference.  Getting a couple of traps for the front corners doesn't have to cost much and can really help.  What kind of speakers are you using?  What is the low frequency -3dB point?  Finally, have you optimized the speaker and listening positions according to the REW room optimizer?  If not, that is the place to start.  Also, before you lock in on traditional room treatments, give the synergistic research black box and HFT products a try.   These things are no joke, they really work, and they have a 30 day return policy.  They are very unobtrusive and WAF friendly.  

@mikexxyz @brownsfan you are correct! I am using a UMIK-1 but it looks like it wasn’t calibrated the first time around. I reinstalled the app and initialized the mic again with the calibration from from MiniDSP. The graph looks much better, though I am surprised about the high end roll off. It sounds pretty clear in the room. To my ear, the lack of bass clarity and generally shy lower mid-bass are the problems. Midbass and highs are actually quite nice to my ear.

I did order a McIntosh MEN220 as well, to help clean it up, but it seems like I’m going to need at least a small amount of bass trapping. My concern with that is that I like bass, and if I add the traps, I would then need to add a sub, which I’d rather not do.

Here is the updated SPL graph:
https://www.dropbox.com/s/wcylhb3pxpmyx82/REW%202.png?dl=0

Here are the waters for full range and just bass
https://www.dropbox.com/s/xvgl22gjo4voxj5/REW%20Waterfall%20Full%20Spectrum.jpg?dl=0

https://www.dropbox.com/s/qa4u37i4r1hrdy7/Rew%20Waterfall.jpg?dl=0

@mayoradamwest, yes, this looks much more reasonable.  Properly placed bass traps will not reduce the amount of bass you perceive from the listening position.  You will place the traps in areas where bass accumulates and does not decay properly.  If you ran an REW sweep with the mic placed in one of the front corners, you would see this.   On the other hand, you have some substantial peaks at about 35 and 50 Hz, and these could be a part of your problem.  But I really encourage you to run the decay waterfall graph on the sweep you just posted.  As I said previously, long decay times below 300 Hz will muddle the bass and that problem will respond to good bass traps.  BTW, I was told by GIF that plus or minus 5 dB is about as good as you can expect to do unless you have a custom built room.  My guess is that you can get to a pretty good place without a lot of money, and you can and probably should add the traps one or two at a time.  These problems are best handled slowly and thoughtfully.  These problems are not the sort of issues you just throw money at and hope for the best.