25 foot bi-wire speaker cables that won't bust the bank?

I have finished upgrading my 2-channel music system. I have an ARCAM CD, Musical Fidelity A3cr pre and power amps connected to Magnepan 1.5/QRs. I use TMC interconnects.

I am still using a single run of original Monster cable (14awg I think) with bananas (speaker) and bare wire(amp). I would really like to upgrade to quality wire and believe bi-wiring makes a big difference with Maggies. My room config requires 25 foot cables.

Audio Advisor is selling off the old MIT Terminator 2 biwires for a good price, but I'm not sure how these are, the Black Box makes me nervous. Other solutions seem problematic (my budget is under $500). Should I use a single run of better cable or a biwire of less expensive ones. Are the MITs really my best bet. Any ideas appreciated (that don't include $1200 worth of cable).