what cable should I buy for my system?

After experiencing the Micca 14-gauge speaker cables ($25, recommended by Steve Huff) and the Belden 5T00UP 10-gauge cables (DIY for $50; BlueJean for $100), I strongly believe that speaker cables can make a significant difference, primarily due to their RCI (resistance, capacitance, and inductance) properties and the geometry of their construction. However, you don't need to spend a fortune to get decent cables that work well with your system.

Although I belong to a different camp, I do agree with Jasonbourne71 that blind testing is essential to achieving an objective assessment of speaker cables—or any cables, for that matter.

Back to your original question, I have had good luck with both WireWorld and Acoustic Zen cables. They both use OCC copper and in every case, excepting power cables, they have made a positive difference when introduced to my system. I have yet to delve seriously into power cables, hence the comment.

And yes, you should consider a separate preamp now, and some digital separates down the road. 

I forgot to add, there is a strong used market for both of these brands, you can save a lot going used. 

use anything that is OCC single crystal wire it is far superior to anything OFC at any price, harmonic technology acoustic Zen are quite reasonable.

I have Bowers speakers and they work really well with Transparent co cables.  Similar to MIT cables.  Located in Maine, Great to talk to on the phone to help.