The Hex codes all look fine. There are two thing to try:

It is possible that the Bryston requires a certain minimum number of repeats, and that the original remote takes care of this. Try sending a larger number of repeats.

The RC5 commands really contains a toggle bit, often called T. It toggles (or should toggle) between 0 and 1 on successive invocations. This is lost when translating to (one) hex signal, since all the generated signals correspond to T = 0 (in general). For example, power on/off with T=1 is

0000 0073 0000 000C 0020 0020 0020 0020 0020 0020 0040 0020 0020 0020 0020 0020 0020 0020 0020 0020 0020 0040 0020 0020 0040 0020 0020 0CC8

Remotes in general handle the toggling in their firmware if told that the signal is RC5, not if presented by just a Pronto Hex. This can probably be done with your remote.