lovinthehd, thanks for your reply.
I do hope someone with experience with both amps would chime in.
Fan noise is not an issue. XLi have its fan always running I think, maybe with variable speed. It is class AB, hence more thermal loss to deal with. From what I have read so far, it isn't audible a few feet away. XLS is apparently quiter, as you have said.
Regardless of whether you are using the crossover or not, DSP is always engaged on the XLS, same as all other series except the XLi. I saw lab tests on the XTi 1000 & XTi 4000 where 10KHz square waves looked like basically sine waves, thanks to the AD-DA conversion. There were some ringing in 1KHz square waves too. Also there is considerable phase rotation on the top octave. Does not mean it will be audible in music playback. But still...
Are you satisfied with the XLS1500s in the high frequencies?