Hi,
Sure, higher wattage is better if the package still fits.? But for audio, I'm be more likely to choose a low-noise bc548 type or a 4401 type (which is a bit beefier and doesn't have the high ft of the 3904.
I'd also change out the biasing diode to some generic silicon 1n4148 etc type as it's reported here that the low audio output can be due to schottky diodes being used there.? I think the preceding stage also sometimes needs to be checked to, as to where the collector voltage is sitting.
73,
Mark.
