Shawndo, I use an old C372 in a 2.1 system. I've tried external crossovers of several flavors, ended up foregoing one altogether (I use sealed mains of the pro studio monitor type that won't go to pieces if fed full range signals, unlike your new KEFs, which I would treat with care if I were you). If I had to do it over, I would consider the C390DD (or the HK990, or an AVR) over the C372 for just these reasons. I'm not putting down the big NAD, it does exactly what it's supposed to, cleanly, with a seemingly bottomless well of power, and has lots of analog connectivity to allow incorporating all sorts of external analog processors to try to kludge things into shape, if you really want to futz around with that. The C390DD brings to the table much more practicality than the old-school NAD integrateds.
The HK 990 does have Audyssey, not sure which version, and comes with built in test tones and a mic. With the NAD you need REW or an Omnimic to determine what's going on (hand held spl meters are rather crude for this), as Grasshopper stated above, and then manually correct for it using the NAD's bass eq features, which are elaborate enough to address most users needs.
If you persist with going with one of the old-school NAD integrateds, I don't believe you need one as big and powerful as the C375. The C326BEE might suffice, and the C356BEE surely would. It's still my feeling that you shouldn't pay for watts you won't need or can't use. Did I mention the C375 is freakin' huge and tends to run hot?