the 27 or 05

Two very different sounding units. The ARC will sound more revealing and articulate, while the Cary will sound more full and musical. You pays your money, you makes your choices.

Neither preamp supports the balanced standard, FWIW... Jmcgrogan2 has got it quite right.

Ralph didn't expand on this point (maybe he was being kind or else explained this elsewhere) but there are many components with XLR connectors that do not necessarily include balanced circuitry.

True balanced requires an additional gain stage. Even without true balanced design, sone might feel there is an advantage simply with the XLR connector over the more common RCA type, others may include XLR for marketing reasons. It is unfortunate all this leads to so much confusion among consumers.

Well Pryso, ... I'm confused by the posts above. Don't know much about the Cary pre. But, it has been said that the ARC LS27 nips at the heels of the Ref 5 (not SE version) and ARC says it sounds better than the venerable Ref 3. Ultimately the choice is with the buyer. The LS27 ain't cheap. If possible I suggest road testing the gear before buying. Wish I could say more, but the only person who can make the call is the guy with the cash.