Agree with Kck on all counts (re: HCA-2). The upper mids on up can be improved, if desired, with simple cap and wire upgrades (see thread at Audio Asylum, or these can be done by a modder like RAM). There's some stiff competition coming out from the likes of Nuforce, Bel Canto, CI Audio and others in the inexpensive but excellent-sounding digital amp parade, but if you're looking used the HCA-2 is tough to beat for the price.
PS audio hca 2 feedback...
I know this has received glowing reviews despite questionable measurements...at any rate...any thoughts? I am looking for a more "modern" sound...speed,detail,transparency,etc....