What version of the switch is this? For 2 pickups or 3?
If it’s for 2 pickups, is it the standard one or the Lee Sklar one?
If it’s for 3 pickups, is it the standard one or the D-Bird one?
In a different price category but the best standalone headphone amp of all time for bass is the Phil Jones BigHead. If you don’t want to pay full retail price, they do pop up once in a blue moon on the used market for around £100-ish.
I used to own 3 of these in various configurations. Now down to 1 but if it weren’t for Covid I’d still own all 3. Frankly the best P basses I’ve ever played. GLWTS sir!
Just to add that when the factory strings die on my Xotic XJ 5er, I’ll be buying another set of Elixir nickels for it. I’m not one who delights in changing strings all the time (unless it’s rounds to flats/tapes or vice-versa for a completely different tone) so these are a no brainer.