Jenneth,
Congrats on your new toy (Stax SRS-4040).

You've just attracted the Stax disease. Since acquiring my Stax system, I'd been on the quest in searching for the 'missing link' to fulfill my musical enjoyment. Of all headphones (ER4S, RS-1 and HD600), the Stax 'phones are by far the most sensitive of the bunch. Here are some cables I've tried: Audioquest(Opal), Kimber Kable KCAG, FMS(Nexus), Harmonic Tech(Silway II), Analysis Oval(Silver) and Stealth M-7. After trying quite a few cables, I ended going for the Granite Audio 470 XLRs:
http://www.graniteaudio.com/cable/page4.html(you can click on the RCA model for their single ended cable).
The Granite cable is made of silver in a process using slow drawn continuous casting to achieve "single-crystal structure". This process is similar to the cables connected to Omega II with an exception of pure copper. Aside from Audioquest and FMS, all other cables are made of silver. In my experiences, silver cables incorporated speed, transparency and details while copper cables exhibited some of those qualities with an overall warmth and perhaps smoothness to the sound. As for the Granite's, it rendered all the qualities of silver cables are known for without the silvery brightness.
If I'm not mistaken, I believe JohnActon has the Kimber Select 1030 for his 4040 and prefer this cable over many others he has tried. Good lucks searching for your cables.