I don't know that I'd necessarily use a divider like that with dual gain pots. Probably not necessary, but there are no rules here. Your second (and first) gain pots are also dividers, just variable. So you're dumping signal in numerous spots. The 150k/ 1nf is a better option in this scenario, in my opinion. But I also don't know the rest of the circuit.
68k/68k is dumping a lot of signal, making for tight bass, a brighter sound and less gain. This is good in a high gain circuit with only one gain pot between v1b and v2a, to control the amount of overall signal in the amp and keep things tight. However, if you now have a gain pot between v1a and v1b, it may no longer be necessary. You can simply run a resistor from the input or output lug of the gain pot to ground to reduce signal to your liking.
The 150k/ 1nf is not a voltage divider. In this case, the 150k is a grid stopper. It's job is reducing very high frequencies and reducing the chances of oscillation. The 1nf to ground is simply removing more highs, albeit lower into the frequency range than the 150k is, from the signal.
