Hello Steve,
Look up several of my threads over the last few years as I have discussed extensively the LS5 which I owned (MK II and later III) along with the PH2 from 1995 to late 2002. I can cover my cable experiences with you in an email exchange. I tried so many and some worked well and others took away all of the LS5's magic. My favorites ended up being the Cardas Golden Cross, SilverAudio and then the NBS Statement. Also, just because a cable is balanced does not mean you can go with a lesser quality! Use the "wrong" cable from the LS5 to your amp, and you will lose much of what you paid for with the LS5.
The original LS5 came out in late 1993. It had 10 tubes but not all 6992s. In 1994 a Mk II version came out which used 10 6922s. Also some other tweaks were made to reduce the noise floor significantly. Then after the Ref1, the MK III followed which used the Ref1's audio circuitry. Many of us who had heard both much preferred the MK III. I think this came out in 1996-1997. The MK III went down to 8 tubes and thus no longer 30db gain but a choice of 12 or 18db set by the factory through resistor changes. And the MK III was a huge refinement as it removed the exaggerated sibilance on the top which made the MK II annoying once you heard the refined MK III. Check out the excellent Robert Harley review in Stereophile, August 1994 and a few followups when the MK II came out.
Concerning the PH2, I feel this was the most neutral product in the ARC line. The PH2 came out in 1992 following the single ended PH1 in 1991. It was so excellent. And with it also being fully balanced, it had a small following which was unfortunate. I tried the PH3 and it was so fatiguing in comparison. I never did try the PH3SE. And of course you will need a tonearm cable with XLR connectors with the PH2. This is no problem with many cable companies that make tonearm cables. Only thing with the PH2 was its 48db of gain which was not enough for my Koetsu Rosewood Sig's low output so I went with a BAT VKP10 phono stage...otherwise I would have never let go of the PH2. The BAT VKP10 too is excellent and does bring on a wee bit more harmonic richness but the PH2's dead silent background made it a resolution marvel.
So check out the many threads and then email me if you are interested in all the details. As you might read, I was a huge fan of the LS5/PH2 but ultimately I encountered the BAT VK31SE and have never looked back.
John