which XLR cables?

The main question to ask yourself, if the run isn't a long one, is: Are my components completely balanced internally so that they'll benefit from using XLR interconnects?

Not sure what you mean by that. Whether or not the components are differentially balanced throughout their internal signal paths is unrelated to the noise and hum reduction benefits that result from having the interface itself balanced. All that is necessary to realize those benefits is that the output stage of the driving component, and the input stage of the destination component (and the cable in between, of course), are balanced.

Balanced internal topology can provide additional benefits, but its absence does not negate the advantages of having the interface itself balanced.

Regards,
-- Al

Viggen900 -- My system has always had just single-ended interconnects, so I can't offer an opinion on your original question. But what might make sense is to experiment with inexpensive but well made xlr cables, such as those used with pro audio gear, and do some comparative listening with respect to single-ended connection before deciding whether or not to invest in more expensive audiophile-oriented xlr cables.

B&H Photo Video has a nice selection of pro-oriented xlr cables, that are generally well constructed (in my experience using some of them with pro audio gear) but very inexpensive:

http://www.bhphotovideo.com/c/shop/4174/Audio_Single_Cables_XLR_to_XLR_Cables.html

Also, on the question of single-ended vs. balanced interfaces, I'd like to add that one circumstance that particularly calls for the use of balanced mode would be if the ac power inputs to the two components are to any degree isolated from one another. Such as by being plugged into separate dedicated ac lines, which is commonly done to prevent cross coupling of digital noise into analog components, or being plugged into isolated outlets on a power conditioner, or because one component is plugged into a power conditioner or surge suppressor and the other (such as a power amp) is not.

While isolating components like that has upsides that are well recognized, it also has the downside of potentially introducing ground offsets between components, which can cause extraneous currents at noise or hum frequencies to flow in interconnect shields. That current would be directly seen as noise or hum by a destination component that is single-ended, but would generally be completely ignored in a balanced interface.

Elizabeth -- Good luck with the nice SP-15 purchase. I don't think you'll find any cheap op amps in there! :)

Regards,
-- Al