When you asked about passive IB-6 wiring one of the first ideas I had was to include a G&L style passive bass cut on some of the designs. The layouts I was going to suggest were:
1) Master volume, 2 volume, 2 tone.
2) Master volume, 2 volume, master tone, master bass cut.
3) 2 volume, 2 tone, master bass cut.
etc.

Note: I'm assuming your diagram is showing the back of the pots.

For the volumes on a bass, typically you wire the 'input' (pickup) to the middle lug and the output on the left lug (as you have drawn them). That allows you to effectively ground a pickup to mute it without affecting the output from the other pup.

The G&L L-series basses used a 0.0022uF cap on their bass cut, but given the range of the 6 string bass I'd probably tend towards a 0047 or even 0068 cap. I've seen a rule of thumb suggesting a bass cut cap should start at 10% of your tone cap value, ie. 0.068uF tone cap would use a 0.0068uF bass cut. Ideally, you would want a revese audio taper 'C' pot for the bass cut so it would work in the same direction as a tone pot, 10 no cut, 0 max cut, and the wiring would be as you've drawn it. You could use a linear 'B' pot, but may be too 'all or nothing' to be useable. If you use a standard audio taper 'A' pot, you'll need to wire the cap and connections between the middle and right lugs, and it will work the opposite way to a tone pot works... in this case, 0 no cut, 10 max cut.

What effect are you trying to achieve with the 'master tone' and 'treble cut' combo? to generally drop some mid to top end with a medium value cap on the master tone and then cut the upper highs further with a smaller value cap treble cut? You would want the treble cut to be wired the same as your master tone between the middle and right lugs, unless you're using a linear or reverse taper pot. There's a chance you won't have fine enough control with both the master tone and treble cut and could double-dip too much with the high end making it too dark, but that's something for your ears to determine.

Instead of using separate tone and treble cut pots you could maybe have one tone pot and use the other pot to sweep between two cap values giving you a variale top end filter for your master tone.