The only way i can connect my headphones to my computer is w/ a headphone extension cord. The computer is underneath and behind a desk. I know its a weird setup...buts the only way it can fit in my room.
 
I currently have a pair of Sony MDR-CD900ST headphones but need some advice on the best headphones extension cord that wont lose anyone of the sound quality. Right now i have a super cheap headphone extension cord from amazon for $5 or $6 (Sound2 Model-S2-EXT6) but I"m sure I'm losing some sound quality from that cheap cord. BTW..I"m buying my roommates Sennheiser HD650's in a couple of weeks. What headphones extension cord should i buy that will be adequate performance wise both my CD900ST and Senn HD650? Thanks.  
 
MDR-CD900ST specifications
 
Type: Closed Dynamic
Frequency response: 5-30,000 Hz
Impedence: 63 Ohms
Max. Input Power: 1,000mW
Plug: Stereo Standard plug
Cord length: 2.5m (Single)
Net weight (without cord): 200g

For $35 Grado is reasonably good for the money.

http://www.amazon.com/gp/product/B001J9BQP4/ref=ord_cart_shr?ie=UTF8&m=ATVPDKIKX0DER

Is there a real difference between cheap headphone extension cords and expensive brand named ones? What should i look for in terms of technical specifications when shopping for a headphone extension cord? Thanks.

I think your cable should sound just fine. If you're just getting into the hobby, making your own cables is easy and educational.