XLR waste of time ?

Yep, I agree with everyone else. Except what Ghostrider says is not totally correct. In fact the Ayre IS a fully balance piece, and in order to take advantage of that you do need to access its XLR inputs and ideally drive it with a balanced signal. If it is wired like my P5Xe phono stage, then the RCA inputs will drive the Ayre in single-ended mode; the RCAs are not wired "like the XLR" inputs. (My p5Xe has switches on the rear panel labeled "BAL" and "UNBAL". You throw the switch based on the input and use the relevant input jacks.) But read the manual on the K5Xe to be sure I am correct. I can only speak about the P5Xe. Its possible that the K5Xe will sound best driven via its XLRs, even though your source component does not output a balanced signal. Charles Hansen probably has an opinion on this.

Jimjoyce, The XLR connector is just a better design than an RCA one. Thinner pins for less eddy current problems, better contact, firmer connection, etc. This is not to say that ALL XLRs will sound better than ALL RCAs, because as you infer there has been quite a lot of development in RCA connectors, largely to overcome their inherent problems. BNC connectors are inherently way better for single-ended audio and should have been the standard, at least for high-end stuff. The RCA connector is only about convenience.

Nrenter makes a great point. I recently found this out when I was ordering a DIN to XLR phono cable from a guy on eBay who makes them cheaper than what I have to pay for the individual parts. He had no idea how to construct a balanced cable, even though he is in the business. He built it to my specs finally, with separate but equal conductors for the positive and negative halves of the signal and the shield separately grounded. I have not done the research to determine whether this problem is common to even megabuck cables. (I paid $70 for the finished cables, which I then terminated myself with my choice of XLRs.)

Dear Gallant_Diva, You wrote, "XLR circuit has two to three times the complexity of RCA, not to take away the transparency and purity of the signal."

That is the old argument for those who believe that single-ended circuits are per se superior to balanced ones, because of lower parts count. I think the argument is spurious, and I could tell you why but it would take too long. Anyway, in the case of the last few posts, we were talking about the relative merits of the two types of connectors (XLR v RCA), as connectors.

Jimjoyce, Your dream of comparing single-ended to balanced under any sort of controlled situation is just a dream. What you could take from this thread are the tips about when you would want to use an XLR connector (in or out) and when it is a waste of time and/or possibly even a detriment. You probably would be best advised to take that information and use it if you are mixing true balanced and SE components in the same system. Otherwise, find what you like and listen to it, single-ended or balanced notwithstanding.

Ralph's remark about the anti-market effect of balanced design reminded me of the time about 10 years or more ago when I was standing in a friend's listening room, which contained many megabuck pieces, and talking with some guys who were in the high-end interconnect business. When they found out I had a balanced preamp (the MP1) they looked at me with nothing short of pity. Didn't I know that a balanced circuit could not possibly sound as good as an SE one, because it had too many parts? I had to walk away to keep from laughing, but there was no reasoning with them.