Would using RCA to XLR conectors screw up sound?

You should keep in mind that you'll likely need a bunch more
swing from the preamp to drive the amp to clipping. This, since you'll be providing 1/2 the p-p voltage swing from the
single ended output. Often, that's not an issue.

The balance of the input circuit can be a minor issue, as
some of the "balanced" inputs are not actually "balanced"-
they are only + & - phase, with different impedances. This,
since the " - " input is often also the node of a diff pair
that gets the *feedback* from the output, and is usually quite
a bit lower in impedance than is the usual " + " or non-
inverting input.As much or more than a full order of magnitude lower in impedance. So, you'd want to be sure
to drive the non-inverting input, given a choice. The other
usually gets grounded.

As mentioned, the common mode noise rejection will be lower,
more like a "regular" amp.

Other than that, it should work ok.

_-_-bear

Chazzbo, not to worry, never heard the slightest difference on VERY resolving speakers. Happy listening!

Many amps today such as the Pass X 600 and 1000, the Nemo's, and many more only have XLR's on them and yet as you have found many great preamps are single ended only.

Here in the showroom with the Pass amps we use the First Sound and Red Rose preamps which are both single ended. We have interconnects custom made with xlr's on one end and
rca's on the other and we also use rca adaptors on the xlr portion of the amps and we have found both to work splendid.

We would not use such a set up on the reference system if it did not sound really spectacular.

I do agree that the key with this set up is how quiet the preamp you use happens to be.

Good luck.

This is a constant topic of debate among local audiophiles here in Phoenix. I own a Rowland Model 2 amplifier. It is fully balanced & has ONLY balanced inputs. I do have balanced to single ended (RCA) adapters, that allow me to use it with preamps that have only RCA outputs.
I'm now using an Adcom GFP 750 preamp. It is fully balanced & also has single ended inputs & outputs.
IF you buy a fully balanced amp & don't use it with a fully balanced preamp, your not taking advantage of all the cicuitry in the amp. The noise floor may go up if you don't stay balanced with the preamp. This is a coin toss-some non-balanced preamps are so quiet the noise floor won't rise anyway..
Read a couple reviews on the amp - see what equipment it was reviewed with. You might even call the manufacturer.
Jeff Rowland & Nelson Pass believe strongly in fully balanced circuits. I met Mr. Rowland at my local dealer. He was very down to earth and easy to talk to.
Try to remember there are amps & preamps that may have balanced inputs & outputs, that are not truly balanced.
You need to verify the "balanced" status by reading the input & output impedence figures.

Daniel