Integrated Amplifiers with neutral sound

This might be overkill as far as power needed, but its smooth, detailed and great bottom end, fits your budget and will drive any speaker in your future.
Coda CSIb

I second Timlub's recommendation. I have had my CODA CSi for about 4 years and still love it.

My Exposure 2010s2 sounds phenomenal with my warm Castles. Entry level Simaudio in it's place sounded too warm and sluggish (though I do have a Simaudio CD player).

That's well below your limit though. In the same vain as Exposure, I would try LFD. Never heard an LFD amp personally, though. Only read about them.

I own a Symphonic Line La Musica amp. Now I have to say this makes me a bit biased but I really think you should put Symphonic Line on your list.

I'm using an ATC SIA2-150 ($4000.00) with a pair of Shelby+Kroll monitors and love the way it sounds. Very clean, neutral, natural, and dynamic. I prefered the ATC over a Pass XA-30.5 and XP-10 preamp combo.
Good-luck