Hey Tex, lets see if I can take these somewhat in order -
First, you're right - you're not that lucky. I only checked the dim's on the tracking room so far, but the sheet I wrote several years ago which only does axial modes, shows that those could be better. What MODESV2 shows includes ALL modes, so the gaps in axial modes aren't causing the Bonello distribution to look as bad as seeing just axial modes. It looks like the tangential and oblique modes may do enough to smooth things out so as not to be too bad. What MODESV2 doesn't mention is that tangential modes are 6 dB weaker than Axial, and Oblique modes are 6 dB weaker than Tangential. This means that your Axial modes will be the primary factor in room colorations, and should be no closer than 5-6 hZ and no farther than about 20. Too close and they cause a peak, too far apart and they cause a hole in the room response.
While the tangential and oblique modes can help fill in response, their lower power means they have less say over the room sound. F. Alton Everest states in several of his books that for rectangular rooms, sometimes it's best to ignore the two lesser types of modes, because "by the time you put furniture and gear in the room, they change anyway..." that's an approximate quote, don't have the books near at the moment.
Corner bass traps usually won't hurt ANY room, but lower freqs get really hard to trap without large dimensions. Couches in general make pretty good bass traps - part of the reason is that they HAVE to stand away from the wall, at least part of the mass anyway - here's why - All walls, including floors and ceilings, are boundarys. By definition, unless a wall allows sound to pass through, there will be maximum sound pressure and minimum air velocity at a boundary. This is why corners are particularly bad for bass buildup - you have three walls coming together at one point, so all 3 dimensions have their peak pressure at the corner, for ALL frequencies that can't pass thru the wall.
The problem is that in order for a material to "absorb" a frequency, the wave must enter the material at near maximum velocity/minimum level, which is just the opposite part of the wave that's available at a boundary. The reason for this is that absorption works by changing acoustic energy into heat - this happens when the wave travels thru a resistance (foam, insulation board, etc) - so, if you put an acoustic resistance across a cavity and seal it so all pressure changes must pass through that acoustic resistance, the frequency that is absorbed most is the one that has its quarter-wavelength at the absorber, relative to the boundary (wall) - as an example, take 80 hZ - wavelength=1130/f, so the wavelength in feet of 80 hZ is 1130/80 or 14.125 feet. Divide by 4 to get 1/4 wavelength, and you have 3.53 feet. A trap for 40 hZ would end up about 7 feet deep.
Now, about that couch - since at least part of it sticks out into the room close to 3 feet, it will tend to absorb some fairly low frequencies because the velocity of the low freqs is high where they enter the couch, so whatever acoustic resistance the couch covering and padding presents to the wave will have much more effect than if the absorbent were right at the wall. Couches aren't generally hermetically sealed, so they won't work as well as a specifically targeted tuned absorber, but they have the added value of comfort factor. If you put the couch in first, you will need less other forms of absorption so it's a good place to start. There isn't really a scientific way to spec out a couch, since they have too many variables as to covering, padding, frames, size, etc -
As to high end absorption, as John says almost everything absorbs highs, including carpet and drapes so generally thicker foam/absorption materials should be used to even out the absorption curve. Check out the SAE site under absorbers, then click on the chart. Look at the different thicknesses of fiberglas board and note that only the 4" board has near perfect absorbtion at 125 hZ. (.99 is considered perfect) - The thicker any material, the lower frequency it will absorb compared to a thinner sample of the same material. this is due to the same phenomenon of zero velocity at boundaries, maximum velocity at 1/4 wavelength mentioned a couple of paragraphs above.
To figure the total absorption at each octave frequency for a room, you need to calculate the total area of walls/floor/ceiling, separated into each type of material, so you can find the total absorption at each frequency band and chart the total room absorption at each octave frequency. I have yet to reach this part in practical application, so I'm probably getting a little vague here.
There is another spreadsheet at
http://www.studiotips.com/
under the Calculation tools heading, download Scott's excel sabin and mode speadsheet. It isn't as self-explanatory as the MODESV2 sheet, so if you're not into spreadsheets it may not help much. Here's what little I know on absorption - 1 sabin is defined as 1 square foot of any material which reflects NOTHING at that particular frequency. A 1 square foot hole in the wall with nothing behind it to bounce things off of, would = 1 sabin at any frequency, while a 1 square foot piece of 2" foam would only be about 0.1 sabin at 125 hZ, but would be much higher at 8 kHz. theoretically, the highest sabin rating of a material can't exceed 1.0 (perfect absorption) but tests of materials sometimes come out higher than that because of boundary diffraction. Most figures are downgraded to .99 even if they test higher, since 1.00 is the highest possible real absorption coefficient.
Once you find out how many sabins at each octave band are present in your room, you can add them up and get an absorption vs. frequency chart of your room. If you have even absorption across the frequency band, the reverb of the room will be un-colored. It may still be too much or too little reverb, depending on the total amount of absorption and your desires for degree of "liveness" in the room. Too much high absorption will leave reverb tails dark and boxy, too much low absorption will suck power out of lower sounds, so you want as even absorption as you can get.
If you like the sound but the RT60 (time it takes for the sound level to be reduced by 60 dB) is too long, you need to add full bandwidth absorption to lower the RT60 without changing the balance - If the RT60 time is too short (reverb decays too soon) you need to liven up some surfaces somehow.
I know this is getting long because I'm getting tired of writing - If you really want lots more, order a copy of F. Alton Everest's Master Handbook of Acoustics, available at Amazon.com if you can't find it locally. Most of what I mentioned is covered in that book, plus a whole lot more.
I'm not trying to put you off, just fading for now - I'll check back on this thread later to see what else you want to cover, or which parts I blew the explanation on and need to re-visit... Steve
I was on 12's 6 days a week for 2 1/2 months this spring. The other depts are on it now. Gets old no matter how good the toys are. I feel for ya guy! Tell us your shopping list! 
No hurry, just curious