Yeah, Mike; the terminology has gotten a bit tangled-up here. As Chris mentioned, there's no "digital" connection in question; these are regular analog left and right channel inputs(which some sub amps do have), as the input to amplifiers has to be(even for those class D amplifiers sometimes incorrectly referred to as "digital").
Also, the "simultaneous" connection isn't to the same speaker, but to the separate sub amp as well as the integrated's internal amp. There's nothing wrong with this, and it's just an internal "Y" arrangement, with one branch feeding the internal amp and a parallel branch going to the pre-outs. A parallel connection doesn't form a voltage divider, and voltage to drive both amps can be supplied without difficulty.
As to the original question about the cables, as has been noted, these are all coaxial cables with RCA plugs on the ends; it doesn't matter if they're called "subwoofer", "RCA", "stereo" or whatever. They do vary in the heaviness of their shielding against outside electrical interference, but the typical cables sold by low-cost providers such as MonoPrice(which I use) are fine for use in nearly all home audio environments. No special "high quality" has to be searched for, as these have all the quality needed for the job.
