I am an expert on audio, certain areas, and this is one of them.
I totally agree with those who say if it ain't broke don't fix it, but, some things are built broke.
To get the best quality integrated audio, which is the type of signal for which this EQ was designed, they chose the wrong frequncies.
Now replacing the power supply filters is probably useless because of the low current drain of the unit, there is simply almost no ripple current to "wear out" the capacitor. However there are other things one can do.
I have modified a couple of these, but then that was for integrated program material, if you use it on a guitar you might want to go a different direction. I don't remember the component values, but once you understand how it works you can do things, many things.
A buddy of mine had his speakers in the corners, which made them very boomy. They have bass, but it is shitty.
At the wiper of the 60Hz control there is a cap, a coil and a resistor. What I did was to take and change that control to about 35Hz and made it shelving, that is to extend the control's range all the way down, instead of that peaked response it originally had. I did this by taking the resistor value down to less than =BD the original and installing a capacitor about ten times the capacity of the original.
The 250Hz control was lowered to about 100Hz by cutting the resistor's value in about =BD and installing a capacitor about three times the original value.
The 1 Khz control was left alone. The 3.5 Khz control had it's range extended slightly downward by increasing the value of it's capacitor.
Finally the 10 Khz control was modified to be shelving, and it's range shifted upward. This brings out the timbre, rather than the tinny treble. This was accomplished by actually lowering the capacitor value as well as the resistor value, and shunting the coil with a low value resistor, about =BC the resistance of the new resistance value in the tuned circuit for that band.
Actually if you know how to futz with it, you could have a nice setup. run the channels in tandem but change some of the frequencies. Lower the low ones on the left and raise the high ones on the right. And if you tandem the channels you also can use a Y adapter to pick off the signal for another amp, between stages.
Tell you what, if you get a chance to play a guitar on two amps at once, enjoy. Set one clean and one fuzzed out. With a little adjusting and practice you can make it sound like you are playing two guitars.