[Coffeemonster]

  If you do not want to spend a lot of money, I'd highly recommend the Fiio E11. It works great on high gain, high power with the 900's.
 
If you have more money, GO-Dap X is a huge step up! Wonderful sound, worth every penny. You might as well get everything you can out of the can.

I'm keeping an eye on the black friday deals (fingers crossed) for a E07k because I want a dac+amp setup. That way I can use it on my work laptop, home pc, and iphone5 (using some solution like on http://www.head-fi.org/t/682222/ios7-iphone-and-apple-cck/180).

 

[Oregonian]

  Also, I am running these with the center hole taped shut. I like the sound better this way, Kees also had the center hole plugged. I think you should try it and see if you like the change!

Got a pic by chance?  I've not modded my Pro900 other than Alpha pads but would consider it.

 

[TWerk]

 
Got a pic by chance?  I've not modded my Pro900 other than Alpha pads but would consider it.

Literally, it is just taking off the pads, and sticking a piece of tape on each side to cover the center hole.
 
When you take off the pads, there should be two black stickers covering two of the 5 holes. Cover the middle holes with tape.

 

[TWerk]

It's barely even a mod haha. It would take all of 20 seconds to do/undo.

 

[TWerk]

  I'm keeping an eye on the black friday deals (fingers crossed) for a E07k because I want a dac+amp setup. That way I can use it on my work laptop, home pc, and iphone5 (using some solution like on http://www.head-fi.org/t/682222/ios7-iphone-and-apple-cck/180).

Yea, the Dac+Amp combo is a good idea for them!

 

[TWerk]

But seriously, if you have a way to get the GO DAP X and it works with how you listen, the thing is amazing. I don't feel like I can do better, and that's a great feeling. 
 
I have always wanted to upgrade everything, which was annoying, but finally, i'm satisfied.

 

[TWerk]

Also, let it again be known the the pro 2900 is spectacular... It improves greatly on the recessed midrange of the pro 900, and decreases the quantity of bass. The treble is outstanding. Owning the two together is a real treat!!
 
But again, these need sufficient power, otherwise you are not going to be able to hear it. Boy, I wish I could just invite some of you over to hear these headphones, it is so amazing.

 

[JIMINITRO]

I just opened mine up and added in that tape. I hear an immediate improvement. I am probably going to experiment more with kees mod when i get more time but these headphones seem to take well to tinkering on first glance over this thread Good god the bass THE BASS

 

[TWerk]

  I just opened mine up and added in that tape. I hear an immediate improvement. I am probably going to experiment more with kees mod when i get more time but these headphones seem to take well to tinkering on first glance over this thread Good god the bass THE BASS

Glad you like the middle hole taped! I do too. To me, it warms the sound a touch, and I like the bass a lot with it.

 

[Coffeemonster]

Glad you like the middle hole taped! I do too. To me, it warms the sound a touch, and I like the bass a lot with it.

Does it matter what type of tape is used? I recall Kee using a felt "sticky tab", has anyone tried electrical/duct/scotch/etc tape?

 

[TWerk]

Does it matter what type of tape is used? I recall Kee using a felt "sticky tab", has anyone tried electrical/duct/scotch/etc tape?

Yea, he used felt. I didn't have felt, so I just plugged the hole with some clear scotch tape. It's still going to block whatever was coming out of the hole.

 

[JIMINITRO]

I used Duct tape. I believe if you use the felt pads like Kees mod it would be similar but the thickness of the felt would definitely dampen it a bit more. 

 

[Hairspray]

  the pro 2900 is spectacular... It improves greatly on the recessed midrange of the pro 900, and decreases the quantity of bass.

 
Would you still describe the 2900 as an open-back basshead HP?
I just can't decide between the two.
I hate recessed mids, but all those posts about the bass perfromance of the 900 are so appealing...

 

[TWerk]

   
Would you still describe the 2900 as an open-back basshead HP?
I just can't decide between the two.
I hate recessed mids, but all those posts about the bass perfromance of the 900 are so appealing...

 
When properly amped, I would indeed call the 2900 a bass-head open-back. But it's more than that. It's like high quality speakers. Something in the treble makes it special, it reaches high and far, and feels very energetic. It is certainly on the sharp side with the treble, so if you were sensitive, I'd be careful. It's very bright! Pro 900 doesn't sound as bright to me, but that's probably because of its HUGE bass.
 
I feel like I'm in the recording studio hearing all kinds of details I've never heard before in any headphone. I started off with the PRO 900, but ever since I got the 2900, I find myself reaching for it more. It's my new favorite hp.
 
It's an outstanding headphone, so incredibly detailed and clear through the whole frequency spectrum.
If you could only have one, and provided you can properly amp it, I'd pick 2900. You could always EQ up the bass a bit if you prefer as well. 
 
For now, I feel like the Pro 900 overwhelms with the bass. The 2900 pulls back in bass (quite a few notches) so you can hear the beauty of the whole song, not primarily booming bass. The bass of the 2900 is still excellent, just smaller (and what headphone isn't if comparing it to the 900?!). The open back also gives it a more airy transparent sound, which makes for an excellent soundstage. 
 
If you "hate" a recessed midrange, I think you should certainly go for the 2900. That's easy. It pushes vocals out further in front than the 900. For me, I love having them both. 

 

[TWerk]

If you have any questions, let me know! 900 and 2900 are both awesome, although very different.