Because of this thread, I tried out my A700s in my MixAmp to do some comparing with some games and movies (namely, Uncharted 2, MGS4, Bad Company 2, Dark Night, Black Hawk Down, Drag Me to Hell) and the A40s compare favourably with the A700s. As for soundstage, yes, I know there's a difference but for the purposes of emulated 5.1 from a Dolby Headphones decoder, open back phones do not work as well as closed back due to how Dolby Headphones 5.1 emulation works. From a purely gamer perspective here, knowing the exact positioning of the audio is absolutely NEEDED for playing games and from that point of view, closed back phones work MUCH better with things like the MixAmp as well as the JVC DH1 (I own both).
Keep in mind, I am in no way talking about enjoying music with these, heck, I haven't tried the A40 with anything else but the PS3 with games and movies. From a purely gaming perspective, the A40+MixAmp I have to say as a full package is the way to go. I had the AX Pros as well, but I returned those and then ordered the A40 + MixAmp. From personal experience with these Dolby Headphone decoders, I actually much prefer the mid-range or slightly lower phones for use with them. There's a very good reason for this, the mid-range or slightly lower phones have the advantage of hiding any of the occasional pops and hisses that both the MixAmp and the JVC DH1 will exhibit (I'm pretty sure it's due to lower quality amps on these decoder boxes). Before the A40s, I was using the A700s with the JVC DH1. I've actually tried and kept using the Ultrasone Pro 650s passed through a Tomahawk amp, not a great experience, there's lots of fidelity but it revealed way too many flaws in the audio track.
I wouldn't compare the A40s to cheap HD201s, I would have to honestly say that they sound like $100 headphones, definitely not $200 headphones (the price you pay for the A40s without the amp). I'm in no way saying that the A40s are great for listening to your music with because there are definitely MUCH better phones out there but then again, I am not a big fan of the A700s either nor was I that big of a fan of the AD700s (I feel my Grados SR80s sounded way better). A900s are much better than both and those I somewhat like (I have a pair of those too but they haven't gotten much use since I have much better phones sitting on my shelf).
As a off to the side note: To be perfectly honest, apart from the soundstage and airiness to the AD700s, the A700s are still comparable and if anything, there's a noticeable better impact with the bass for the A700s. Doesn't mean that the AD700s are lacking bass, it just means it doesn't hit as hard.