I extensively listened to the A21 when I was purchasing a new amp. I took a leap of faith and had Odyssey custom build my amp to exactly what I wanted. I took delivery of the Stratos amp 3 years ago and I have no desire to get something better. The Odyssey amp walks all over the Parasound. In my system and with my music, the Parasound sounded very powerful but a little light or lean sounding. In other words, there was a lot of power, but just a little less than ideal weight to the music.
The Odyssey leans on the slightly warm side and it is very powerful. I have it coupled to a Modulus 3B tube preamp and the sound is heavenly. The only drawback to buying the Odyssey is if you are purchasing it new from the factory, the wait time is very long. If you are like me and impatient, that could be a problem. I was so excited to finally get my new amp that on the day of delivery, I played hooky from work so I could play with it.