These boards, driven by an smps600rxe (have not tried the smps500rxe), sound like an exellent class-a amplifier, without the heat or the weight.
The Anthony Gallo 3.1 is known as a current-hungry speaker. The cxd250-hp board does a very good job at making the bass tight and tuneful.
But the best of this amplifier is in the highs. The top end is smooth, extremely well defined and transparent, as well as able to produce a very convincing soundstage. The band is in the room. The timbres are as convincing. Xylophone and piano sound wonderfull, saxophone as well. Decays last for as long as they need to and you get all the echos of the recording room. To sum it up: very accurate and refined highs. The specification mentions 0.002% of distorsion at more than half of rated power. My ears tell me there is no reason whatsoever to doubt this impressive figure.
The sound is much like an excellent tube amplifier. Accurate, never harsh, with a very expressive medium. And very good control in the bass, pretty close to the ultimate with proper wire gauge (I used 16 gauge, 22 amp rated for all high-voltage connections).
Simply one of the best amplifier i have had the chance to audition. And it runs cool!
At this price, 500$ usd, including all required material, it is a very rare bargain. Plus, the boards look great. With the layout and wire choice i have made, my amplifier looks like a work of art inside. Like a high-end power amplifier. For just 500$ plus of course approximately 12 hours of labour, especially hard and painful when crimping high-end wire for the molex signal connectors.
Please take note that you need excellent equipment upstream to appreciate the full extent of this amplifier's excellence.
Compared to the cxd500, cxd250hp has basically the same signature but has a bit less punch. However, it is a significantly better amplifier because of the extremely refined highs, which provide better resolution and stereo image.
I recommend a balanced connection to minimize the noise floor, which is low with my 89db Gallos connected this way. I did not use shielded signal cable inside my amplifier, a single-ended connection would most likely be good enough if it was the case. Note that you can always use an rca to xlr adapter and shielded balanced wiring inside, which would be best. The layout is important, use star-shaped power distribution with even path when powering two amp board with one supply and try minimize the signal path. Invert polarity at the signal input and speaker output on one of the board to help prevent bus pumping.
Associated equipment: mac mini ssd 8gb, schiit wyrd, audio-gd master-7, di2014 and master-1.
Rating: [5 of 5 Stars!]