I am not sure where the blame lies. For those systems that have impactful bass, they were all using much bigger subwoofers than mine - one guy has four 15" subs, and another has two subwoofers, with each subwoofer containing 3x 12" drivers. So I am not sure whether my result is due to using smaller subs, or whether it is because my bass is too dry.
Taking into account the above, I think you have a couple of issues going on as many others have mentioned. First off you have to EQ the subs a little (or a lot) hotter than what your graphs show. Also, many times when subs are pushed to the limit, they can become a one note sound. So, since the room size that you mention is large with the subs you have. I would say your lacking in size and power. Get much more powerful subs as you have to pressurize the entire room. This can be done in pretty much any scenario with enough money. So with your large window letting some pressure out you just have to kick it up a notch. How to do this cheaply? I don't think you can. Large rooms require large powerful subs to get the required pressurization. I would check Sweetchaos (I think that is his name) sub rankings and look to massive output from 25 to 50hz. Also look at ported subs, most sealed will not give you want you want unless you spend even more money! So, you want to get a kick in the chest, crack paint on the walls and destroy light bulbs? How much money do you have?
All in all it can be done. You just have some large room issues with that large window port lowering your pressurization ability. I would fiddle with it until you know your subs are just not keeping up and then make a decision to replace all of them for
much bigger, more powerful subs. Good Luck and let us know if you "crack the code" without buying new subs. We all learn from someone actually doing it.