I would not get a Matrix DAC for headphones maybe too bright.
I am currently listening to the RME DAC that I got for free (available used for $500-700). I am very impressed by this DAC on the phones. Now I am comparing this to a $12k DAC I had on it yesterday, but this RME is really solid and will likely be my office DAC, for headphones and 2-channel.
I got a Schiit Byggy DAC coming in next week. I have been saying that for 3 weeks now. The RME has impressed me to the point that I am feeling more confident about selling the Byggy DAC at over $3k. If the free DAC is almost as good as the $3k DAC, I would rather pocket the $3k.
If I were you, I would get a used RAAL SR1a with the special Schiit RAAL amp as a starter set. When you realize how great that thing is you can explore better amps. I am using a Schitt Aegir v1 amp that is 20-watts Class A. I got this amp used for $400 and today the RME DAC.
The SR1a will get you closer to 2-channel speakers more than almost every headphone. The MySphere may be similar. I just sold a $7k tube amp to go with the $400 Aegir v1. I also decided to go with the SR1a over the $12k RAAL 1995 Immanis because I am a 2-channel person and the SR1a (or SR1b) is almost 2-channel.

