Which is the best cable for Martin-Logan?

I will only recomend only one cabel..Transparent Audio and that best match for them.

Having owned the Quest Z's myself, I experimented with many different cables with them. Monster Sigma Reference, JPS Labs Superconductors, etc. The JPS cable will provide adequate performance levels. They are extremely neutral, and JPS offers a bi-wired version if you desire to bi-wire the Quests. However, no other speaker cable has come close to providing the performance that my current Transparent Audio Wave Ultras provide. These cables have brought the greatest single improvement to date within my system. They are pricey to be certain, but these are the only cables I know of which deliver the goods. If you really want to hear what your Quests are capable of, experiment with a pair of Wave Ultras yourself. You'll find them used for around $900 for an 8' pair. About the price of an average CD player, but providing far greater benefits. The gentleman who suggested checking your distance to the front wall provided you valuable information as well. Proper set-up with any Martin Logan speaker is absolutely critical. They will require breathing room. Having said that, I actually sold my Quest Z's simply because I found they were actually too large for my modest 15'x 20' room. The SL3's and Aerius I's both provide much better performance and dynamics in this room than the Quest Z's were able to. Enjoy!

I purchased a pair of reQuests last year and tried the following cable Manufacturers: Transparent, Cardas, Goertz, JPS Labs, D. H. Labs and Harmonic Technology. Although each different cable had a positive virtue or two, only one released the "magic" hidden in the reQuests. The Harmonic Technology speaker cable was dead even or clearly superior in all categories to all the other cables. It was so good that I upgraded all of my interconnects and power cords as well. The speaker cables were about $900 per 8 ft. pair(bi-wired) and the interconnects were $250. The power cords were $180. The "single crystal" design of all of their products is simply a result of a better manufacturing process that leads to superior sonic results. Since the reQuests have to be plugged-in, I would reccommend buying the power cords first. The interconnects second, and finally the speaker cables last. Jim Wang of Harmonic Technology suggested that strategy for me and the incremental changes were astonishing.

What about..MIT MH 750 bi...?

Since you have already had many responses, I am not going to offer any specific recommendations except for power cords. In my opinion and the opinion of Audio Research, the best power cords are from Aural Symphonics (Univocal). I was not ready for the improvement, especially on digital sources and preamp. Amazingly, they make a major difference on ML's as well. A general piece of advise. All audio systems are just that, systems made up of components that all have some type of skew. Use the cable to tune to your tastes, but insure that the capacitance is right for your needs or you will be inserting the equivalent of a high pass filter between components and roll off the highs. The other issue is phase coherency. Most of the recent better cables are fairly phase coherent (improved resolution). Regarding Monster. I am not a big fan, although their M2.4 biwire speaker wire is a steal for a cable that is probably almost as good as the absurdly priced Transparent cables which are merely good wire with a Zobel network on the end to stablize impedence.