Gibson's 2 Vol and 2 Tone controls - more is less: Ohm's Law states that resistance is halved when two pots of equal value are connected in parallel. That means when two pickups are switched on together their respective 350K Ohm volume pots resolve (halve) to 175K Ohms. Humbuckers sound their most clear and most dynamic with a 500k volume pot and clarity and dynamic response was compromised when Gibson changed to 350K pots. Furthermore, the sound increasingly turns to mud when both pickups are switched ON together and the load resistance resolves to a far-too-low 175K Ohms. Kinman recommends 500k pots for our Humbuckers, and a single one is better than two.
A similar situation occurs with Tone pots too because two 0.022 uF capacitors are connected in parallel when both pickups are switched on together and the capacitance resolves (doubles) to 0.044uF if both Tone controls are turned down. This is highly undesirable because it causes massive loss or treble, presence and definition and results in MUD. Kinman recommends to remove one Capacitor from Gibson guitars and re-connect the remaining one to both Tone controls the way Fender do.
Fender single Vol and 2 Tone controls- less is better:
Leo Fender was being frugal when he specified a single volume control. But, unknowingly, he caused a great benefit to guitar players many years later by doing this (especially Mark Knopfler). See, the Stratocaster's 3 pickups operating into a single 250k volume control are never loaded by less than 250K Ohms and this allows position 2 and 4 to operate with the ideal 250K Ohm load of the single volume control. A further benefit is that the two Tone controls share a single capacitor (unlike Gibson which have 2 caps). The single shared Capacitor means the sound will never see more than 0.022uF and will never resolve to more than that even if both tone controls are turned down (0.44uF or 0.066uF) with sudden change of switch positions, as Gibson's do.
It's a case of less is clearly better.
Knowing what Gibson's 2 volume controls and 2 tone controls do when 2 pickups are engaged it's easy to see why we believe single Volume and Tone controls are your best option. Problem is what to do with the other existing volume and tone controls? Splitting switches for both humbuckers perhaps? But what about if the pickups are P-90's and don't split? Now that's a problem that calls for creative thinking.