Team212 gives good advice, because if you want to change to XLR on your amp, you would have to drill bigger holes for them, apart from un- and resoldering your connections. Adapters are expensive and especially if you have a high resolution system, they sometimes degrade the sound. Not always though, also here the proof lies in the listening. Camac/Fisher were certainly better than the common run RCA stuff, but good Neutric XLR is excellent soundwise as well.
Should you wish to do as Des suggests, see to it, that you get a really good technician, because soldering high end ICs can sometimes be a very tricky job. If you cannot find an expert, whom you trust, to do this for you, I'd rather suggest method one, doing the changes for XLR on amp and preamp. You'd have to do some drilling on the chassis, but the soldering is less tricky. If you have the top gold-silver Siltech IC, I would not touch them, but definitely do the change on the respective chassis. If your cable is less tricky, I'd do as Des suggests. Just my usual 2cents.
Should you wish to do as Des suggests, see to it, that you get a really good technician, because soldering high end ICs can sometimes be a very tricky job. If you cannot find an expert, whom you trust, to do this for you, I'd rather suggest method one, doing the changes for XLR on amp and preamp. You'd have to do some drilling on the chassis, but the soldering is less tricky. If you have the top gold-silver Siltech IC, I would not touch them, but definitely do the change on the respective chassis. If your cable is less tricky, I'd do as Des suggests. Just my usual 2cents.