Alan,
Due to the reverse polarity, the sound image you hear would most likely be out of phase and sounded diffused. There are a few things you can do:
1. Reverse speaker wires' + and - connections to the speakers. This is the cheapest approach. However, this assumes you have no other source components in your system. Otherwise, you will need to switch the speaker wires back normal when listening from other sources. Remember to turn the amp off while attempting this.
2. I don't remember that Krell 400xi has this function. But on some preamp, they have a reverse polarity switch. If you like SA11, that may be something to consider for the next upgrade.
3. If the XLR cables are purchased new from a dealer, you should be able to request a custom-made with reverse of polarity. -- not recommended.
4. If you are going to send the unit for mod, it would be a good idea to ask the modder to reverse polarity for you.
5. Just stay with single ended RCA and make your life easier. However, many true balanced design gears sound better (to various degree) when connected XLR.
Hopefully this will give some insights. Many European gears and some US gears (such as Jeff Rowland) also have the polarity reversed. Good luck.