Hi Giololucas
I understand that it will be a completely waste of money on using fast recovery diodes on amplifiers psu, as almost all high end gear has standard diodes. But there is two considerations i have, standard recovery diodes has a small spike on every cycle when them shut down when analized on the scope, wich is not an issue at all because you can use a snubber to avoid that spike. As you are on a DIY enviroment, when a cost of some extra bucks on the PSU in not an issue, you can make a "Noise Free" PSU to ensure that if you have a problem is not on the psu, thats why i use fast recovery diodes with a 100uf snubbers on each diode to make it even faster, and i see no spike on the scope.
The second consideration is when you are on a production enviroment, when every cent worth on the work production, there were prototipes made and the amplifier is tested and there is no issues with the amplifier and the psu, a use of standard diodes and a single snubber for the for diodes will reduce the costs significantly.
It's a matter of choice, and remember, those spikes are only seen on the scope, you will not hear them on the speaker, but for project, it can generate noises on the rest of the circuit that you will hear and will not understand where it come from.
Hope this help
Best Regards
Lira