After some discussion, my friend loaned me his James Romeyn Class D mono block Hypex NC400 power amplifiers and I liked them very much. They sounded much better than my Luxman 590ax Class A integrated amplifier. The music was more open, detailed with much improved bass. I was very surprised and could not believe it.
I consulted with James Romeyn and decided to buy his Hypex NCore NC400 dual mono block power amplifiers with 2 NC400 amps per side with the NC1200 power supply. He recommended his Class D dual mono version for improved sound quality.
The amplifiers finally arrived and they were a step above his mono block power amplifiers. The sound quality from my Hypex NCore NC400 Class D duel mono block power amplifiers is amazing.
My sound system sounds much improved over my Luxman 590ax Class A integrated amplifier. I am hearing details, imaging and bass that I have not heard before. My system now offers breath taking detail, transparency, lack of noise, and excellent dynamics that I did not hear with the Luxman 590axClass A integrated amplifier.
I purchased the Hypex NCore Class D amps from James Romeyn Music andAudio, LLC (James). He was very helpful answering my many questions and I suggest you contact him for more information on his assembled Hypex amplifiers (he offers 3 models at different price levels). The dual mono version is $2,980. See:
http://jamesromeyn.com/product/hypex-professional-build-service/#tab-description
Eventually, I replaced my Hypex NCore NC400 dual mono block power amplifiers with the Mola Mola Kaluga power amplifiers. These amplifiers use the Hypex NC1200 and NC1200 power supply custom built by Bruno Putzeys at Mola Mola. The Mola Mola power amp is excellent and highly recommended.
https://www.mola-mola.nl/kaluga.php