Thanks for the advice, I'll keep that in mind. So you think a headphone upgrade would be more beneficial? If so could you advise a couple of options?
As long as you're already using ASIO or WASAPI (or, Kernel Streaming, i.e. any kind of bit-perfect) output in Foobar2000 rather than Direct Sound, then yes, you will get MUCH more of a benefit from upgrading to better headphones than from getting a DAC/Amp. If you're NOT already using bit-perfect output, do some research on ASIO, WASAPI, and Kernel Streaming (and how to get them in Foobar2000) and start using them right away!
About the over-ear Momentums in-particular. . .they are, in my experience, QUITE overrated, unfortunately. I feel like Sennheiser actually missed the mark on them. . .they sound incredibly dull to me due to the lack of soundstage and imaging. And the idea that they "need an amp to sound best" is kind of silly, they have an 18ohm impedance and 200mW power-handling rating so just about anything can easily drive them to their maximum potential.k They sounded quite sub-par on my Fiio X3ii DAP, which has a much better amp section than what is found in more "mainstream" (iPod and such) music players.
That being said, you still WILL get a very noticable benefit, as well, from a better DAC (USB-connected, external) unless your computer happens to have unusually good onboard audio, which it almost definitely does not. I notice a BIG difference between the sound in Foobar2000 with bit-perfect output through my motherboard's onboard sound, and the sound I get when using my Fiio X3 2nd Generation portable player as an external DAC. And I'm not using fancy-schmancy high-end headphones, just some mid-range on-ears, the V-Moda Crossfade M-80, and I still notice a big sound improvement with the use of an external DAC. If you get a DAC, you would want to get something Asynchronous as well as Power-Isolated, ideally, in order tog ive the biggest improvement over onboard sound. Personally I am looking to get the HiFiMeDIY UAE23+ DAC, it's available for 89.99 and is supposed to be one fo the best options for under a hundred dollars, and uses components (Sabre ES9023 chip, for example) taht normally tend to be found in much higher-priced units from other companies.
As folks are saying, the priority should be first headphones, then Amp/DAC (with no need for amp depending what headphones you do get), with the added caveat of making sure to always use ASIO, WASAPI, or Kernel Streaming for bit-perfect output in Foobar2000. Some good headphones in the 100-to-200 dollar price-range would be the V-Moda M-80 or V-Moda XS on-ears (I love my M-80s for the price), and for the price-range going higher than the Momentums by a bit, you could get the Sony MDR-1A (for a more colored response) or PSB M4U 1 (for a flatter response) which both sound waaaay better than the Momentums. I hear the Audio Technica ATH-MSR7 are also great if you don't mind a brighter sound, and Music Alchemist here continues swearing by the Yamaha HPH MT220 for non-electrostats whenever folks ask him for recommendations, and as someone who apparently tends to listen to VERY high-end electrostat headphones from Stax, I'd guess that if he says something sounds good, it must be true
You could also go with the option of something open-backed if you feel you don't need isolation, you'll get a more natural sound that way.
. Just know that once you start getting near / above the $300 range, chances are you'll want dedicated gear to drive those cans. It's kind of a hidden cost. To get a big upgrade from Momentums, going to something like the B&W P7 might be fine without a dedicated amp, but the AKG K712 or so would need one. A clean DAC almost always helps, IME.
