I'm not sure what exactly is going here... but here's a little suggestion.
http://www.amazon.com/digiZoid-zo-2-ZO-2/dp/B00747N5ZE/ref=sr_1_1?ie=UTF8&qid=1332918669&sr=8-1
Whether one's a bass lover or not.. this little monster is small, but POWERFUL.
I've hooked up my Shure 440's to it and played some electronic Dance track. This little amp has about 20+ settings and 2 or 3 different EQ settings for each... which makes it about 40+ presets..
And trust me, I went all the way up in terms of bass. And the shures... well let's just say that they didn't sound like Shure SRH440's anymore, rather some Hybrid of 440's clarity and precision with Sony MDRXB1000's Bass signature. It was unreal.. And the best part, no distortion what's or ever. And I think it holds its own as far as 300ohm of impedance headphones.
Just in case someone wants his Neutral Analytical sound Sig with MegaBass without compromising the spectrum... there ya go..
As for the 840's, bassier than the 440's and extend slightly better in the lower sub-bass FR. Not as neutral though. 440's are regarded as the most balanced of the SRH lineup (less the new ones).
And the HD800 don't have too little bass, they're simply geared for different music Genre's. They're definitely not Neutral Sounding headphone. However they are natural sounding, very laid back, power hungry and very very spacious. I can't see them doing justice to Metal, Rock, Alternative or anything grungy that has that in your face forward sound. And don't even think of putting Pop or any Electronic or remotely electronic based music, including Rap/HipHop or R&B. Oldies, Blues, Jazz, Soft Acoustics and Soft music and Classical... that's where the HD800 belong. And yes, properly amped, they will do better for these types of music than any other headphone that I have heard. Though I will say that the SRH940 weren't too far behind... which is saying a LOT about a $300 pinned against a $1500 monster.
Peace