What Gauge of Wire...?

Depends how long the runs of speaker wire are. 12 gauge should suffice. If you can keep them short enough 14 shouldn't be an issue.

Paul Speltz anti cables.....One of the best bargains out there...( 12gauge solid core )

No thicker than 12 though, 14 is fine it will generally be faster possibly better resolution. You would be surprised that a "relatively" thin gauge would be better compared to all those fire hoses that are being pushed. If you look at the leads after cutting away the Insulating fillers and rfi rmi rejection layers that the wires are the same 14G size mutifilaments you take off the lamp wire spindle.
However if you want something really different and can percieve 1 part in a million impurity get the 8 "nines" wires. I can't hear it, but different coppers do seem to have an impact e.g. single crystal (OHNO) cast copper.
It is difficult to dissect the changesimposed by the hoses from the metals. I do think that silver is really quite different sounding than copper. People wiser than I say the usual cliches are bull. I can't understand why silver wires do have a sonic character in virtually every instance that I employ them that is reproducible in my mind all Physics aside. Except for the very least expensive ICs silver is not a budget friendly choice, nor is any patented alloy using Silver, Irridium , Palladium, Platinum, Tantulum, tempertamperum, Gold, Molybdenem......even aluminum is going to multiply the cost to high to stratospheric levels.

BTW avoid the heavy metals the radiation (gamma) makes me nauseas.
That said Wire does make your system sound different. I didn't believe it so me and my equally skeptical buddy tried out a good selection of speaker cables and the differences weren't subtle. The good part was -for that system,- on that day we agreed completely on the winner. It was of course the least expensive cable in the pile. (No Lamp Cord was tried as I recall sorry)

Hi Tiko , I had much the same speaker set up as yours but was using an Onkyo TX-DS939 Receiver and NHT Hdmp2 dipoles for the rears . I never found a high priced speaker cable of any gauge that could even justify the price versus performance with the NHT set up for Home Theater. I ended up using and was more than happy with audio quest cv4 that I bought a bulk roll for under a hundred bucks then used those 4 dollar a pair deltron banana connectors . When I changed homes and re-set up the system in a room with wall to wall carpet I used a bulk roll of monster flat line tucked under the base boards and carpet and it sounded great as well . Unless the metal tweeters in the fronts are giving you too much zing what your using will be fine . I found that the inter-connects in my system made more of a differance in quality of sound than the speaker wires did with the NHTs .(Van den hull Mk11) Or at least they tamed the metal tweeters a little better than they already are . Cheers.