All the mods I did were thermal/mechanical, didn't change anything with regards to the stock electronic board circuit - the opamps plug into 8 pin socket connectors on the board. Heat sinks were selected and adhered to the transistors that needed them.
The reason I ended up choosing the Gustard H10 was actually got a Massdrop email about a drop for it and then researched it. This was after hearing high current amps at a headphone meet with my TH-X00PH and M1060 and wanting to look into higher powered amps. Experimenting with opamps and being able to alter the sound with them was a big draw as was its really low output resistance and high praise of its dynamics, clarity, and detail with Burson opamps. The one thing that had me nervous was the heat related failure issues with the Burson V5 opamps... they simply were not reliable stuffed inside the closed H10 chassis and would fail from heat buildup. Decided to get the H10 anyways (bought 2 in the drop actually) with plans to mod it to reduce heat on the components, which is what I did. I ran it with the top off until the mods were completed so it would help out the two voltage regulators which were identified as the main components that needed some thermal help.
I was looking into the H20 as well, but it seems to have gone a different direction from the H10, with a different sound and not really designed for rolling opamps. Absolutely love the sound the H10 provides and will stick with it, it works great with all my dynamics and planars.
Whatever amp you go with I would suggest something on the warmish side that also is known for excellent detail, dynamics, and clarity. I previously thought that a neutral amp was my ideal, but the Meier Audio JAZZ-ff I had showed me that no matter how clear and detailed it was, it just didn't sync with me - my headphones always somehow felt lacking in bass presence/impact and dynamics. The H10 cured the lack of bass and dynamics for my phones while also adding in even more detail than I heard from them before.