I don't know why technically the H Bridge overheats with capacitance, but I know it does.
I started using that particular H Bridge as that is what Mike Zemek, the initial designer of the successful and reliable RCS system, specified. We tried a number of methods trying to convert the output to linear DC and each one caused the H Bridge to overheat.
I also tried a DCC based "filtering" but that was many years ago and was mainly tried to get rid of the Buzzz associated with the low frequency pulse I first used on FET / Relay ESC's I made at the time. Nowadays of course the PWM frequency has been raised to be more or less out of the range of human hearing for most people.
I do make a Linear out ESC that converts the pwm output of the IC I use to filtered DC. I use a voltage multiplier circuit to raise the the voltage form the 5 volt logic up to a maximum of 20 volts. It is that 10 amp ESC that I successfully used for testing with a QSI sound decoder in a GP-40 a few months ago.
I don't think the effort required to rewrite the current operating program to provide timed pulses for blowing the Horn/Whistle and triggering the bell is worth it, given that I understand that QSI are rumoured to be modifying the decoder to read trigger outputs. If that upgrade eventuates I may develop the system further.