Re: F25
I have dual F12's and I can't ever see needing more bass even in a very big room like I'm in now. I have them set at 12 o'clock and -9 dB in Audyssey, so they have a lot more room to go. When I turn them up they make the whole house shake during reference level movies. I mean it's intense, it scares the daylights out of people and you can feel your chest moving. I sorta find it difficult to believe that there is such lacking bass with one sub. You may want to buy another one and see if you can even out the room modes that way. It would make more sense that you are just experiencing lackluster subwoofer placement due to room compromises. A second 12" sub would be much cheaper and would be more likely to solve any room mode issues you might be experiencing.
A sub crawl, when in doubt, is always recommended as well. I've read some crazy stories of people getting massive improvements in subwoofer performance after a sub crawl. This assumes that you are able to place the sub in the spot where you find the best sound. Usually that isn't the case, and that's where a second sub can really help out, again if you have space.
-Alex
PS4/Nvidia Shield --> Emotiva XMC-1 --> Emotiva XPA-5 --> Ascend Acoustics Sierra Towers and Horizon Center w/ RAAL tweeters (L/C/R), HTM-200 SE (Surrounds), 2x Rythmik F12 subwoofers