My Parasound pre-amp has a balance control. The only time I use the balance control is about 4 times a year to make sure the potentiometer isn't getting dirty/scratchy. I don't know if it's sealed or not.
My KEF's have a wide soundstage, so the sweet spot is huge, so the left-right balance has never been an issue.
My Parasound has (horrors or horrors) tone controls for bass and treble. I occasionally use the bass tone control to boost or cut the bass 1 or 2 clicks. I don't like tweaking my subwoofer levels. Most of the time, I run the pre-amp in the mode that bypasses the tone controls.
If I remember correctly, the bass tone control is centered at 150 or 200 hz. It's lower than the typically low-end Japanese audio tone control.
Hsvheelfan