I don't have any issues needing SPL attenuation.
Would a pair of resistors between the speaker taps and headphone jacks knock out the hum? If so, what type and Ohms should I use?
Otherwise, I'm very happy with the sound.
I'm not sure if resistors would fix your problem, but if you want to try using series resistors, you can figure out the ohm value to use with this formula.
Output power in watts = ((20* headphone impedance)/( resistor impedance + headphone impedance))^2 / headphone impedance.
Instead of trying to solve that thing algebraically, I'd suggest plugging in your headphone impedance and then graphing the function using something like fooplot (free website).
Robrob has some more in-depth formulas for other types of resistor networks that give you SPL attenuation instead of just output power.
Use the right side of the graphic. 110 ohm resistors on the two + headphone wires will give you 12dB of attenuation which is about the minimum I'd recommend anyone start with, so 100 to 200 ohm 3 watt resistors is my recommendation. One resistor attenuation like this is usually fine for solid state amps but for any tube amp I'd recommend you go with the left side of the graphic's two resistor network to match the amp's expected speaker load.
The headphone impedance has very little effect on the one or two resistor setups in the graphic so just ignore it.
Insert the resistors in the left + and right + headphone wires any way you care to do it.
Then I will have to thank the OP, M-13 and a few others to carry on the hype train so that I could be annoyed enough to try this little amp out. For the part $ and how long it takes if you have the tools, it's silly not to mod this amp. I am glad it worked out for you as it did for me.
I should have taken a picture of it, but all we did was cut the wire ahead of the spade connector (on both the right and left positive leads) and solder on a 150ohm resistor in series to each lead. All covered up with heat shrink.