The value and the resistance (impedance) that the unit feeds forms a high pass filter. Generally PJ designs for a roll off that hits at a very low frequency, something like 5 Hz, or 3 Hz. The larger the capacitor value is the lower the frequency starts to roll off. So Bottlehead chooses a reasonably low frequency. A larger capacitor passes lower frequencies but everything is flat above the roll off. None of those frequencies that a larger cap would pass are musical notes.
Then there is a problem that crops up with really large capacitors, the windings are inductive. But none of us would be putting this large a capacitor on the Seduction.
I read sometime just after the release of the Eros that it was designed with a 0.47uF capacitor for the output and the 1.0uF Solen was an upgrade in quality, but not because of the increase in value. The capacitor they use is already stocked for another unit.
I would have to disagree that an increased output cap, at least in the circuitry I have seen, would emphasize the bass. Larger caps allow lower notes, in this case noise, to pass.
I hope that explains what you were looking for.
