It depends if you are only interested in correcting for a small listening sweet spot (two seats next to each other) or are you attempting to obtain an acceptable response over a much larger listening area. If you are only concern with those two seated positions you plotted for (my guess is they are fairly closely located to each other.. perhaps within three feet of and possibly side-by-side) then Audyssey should do a fine job of coming up with a compromise that will be quite good. However if you intend to use Audyssey to find a compromise for a much larger area then you would need to map all those listening locations to be sure you indeed have selected the best sub position... this is where you will definitely find REW a blessing. I think the time savings alone from 'mapping' out 8 listening positions X say 4 different sub positions "by hand" using single Hz test tones from 10-120Hz might make it worth spending the effort and time needed to learn how to use REW. I'm guessing producing 32 separate SPLxfreq maps using your current methodology would consume many hours of tedious measureing and hand plotting the single Hz test tones, whereas REW could plot each set of 8 listening positions in about a minute for each of the sub positions. PLUS you can manipulate the graphs in so many ways it would take me too long to list... but Don has already given you the best part... the fine resolution detail of the freq response and of course the info on time domain freq response, which will also allow you to assess and 'tune' your room. It really is worth the effort to download the software and tutorial and learn how to use it.