These speakers are indeed revealing... which calls for quality DACs and preamp/amp. The NHT2.5i can be biamped quite easily... and I know of many who used tube amps for highs/midrange and a solid state for the bass. I don't know your budget, but I would recommend a used Peachtree Decco integrated, which has a usb dac and tube pre-amp section. I've seen these go for about $450-500 used here on audiogon. However, the power amp section is about 40-50 watts and would probably not provide enough juice for the power hungry bass drivers.... you could use the pre-outs and biamp with a Tim Rawson gainclone... these have surprisingly strong bass and come up used here on audiogon for as low as $200.
Good luck!
Good luck!