Arne Aas wrote:

Does anyone have any recommendation regarding the PS Audio HCA-2 vs.
the TacT SDA2175?

Yes, avoid them both.

Switchmode power amps generally have complex L-C ultrasonic filters on
their outputs, which are required to keep them from spewing RF all over the
place, inciting the FCC to ban the equipment, and frying tweeters. These
filters tend to significantly raise the output impedance of the power amp
near the high end of the audio band and make the timbre of the amplifier
extraodinarily dependent on the impedance curve of the speakers they drive.

You can see this effect in figure 1 at
http://www.stereophile.com/amplifica...29/index8.html . This graph
understates the problem somewhat, because Stereophile's simulated
loudspeaker load is definitely wimpy compared to the high end speakers that
they have tested.

You can also discount the entire Kal Rubinson review because this
once-sensible reviewer has lost his mind and bought into magic power cord
hysteria:

http://www.stereophile.com/amplifica...29/index5.html

"I'd been using PS Audio's Lab Cable 2 instead of the standard IEC cord
supplied with the HCA-2. Using the regular cord flattened that generous
depth of image without affecting the amp's other performance aspects."