What vol for a second (or further) bleaching?

There are two light blonde XXL dyes, one has 30 vol and one has 40. Hi Lift blondes never give the amount of lift they promise IME, and XXL is one of the better ones.
If you want a lot of lift you would be better off with a good bleach powder and peroxide. You get a lot more lift for a similar amount of damage.

Yeah, 00A Absolute Platinum and 00B Max Blonde ... I used the 00B which I think is the stronger one.  Guess I'll leave it in the cupboard.

I've got Matrix Light Master bleach powder in my virtual shopping basket, but does it matter what brand of developer I get?  Is Truzone ok?

I think bleach powder is more important than developer. I just use any old developer.

I've got Matrix Light Master bleach powder in my virtual shopping basket, but does it matter what brand of developer I get?  Is Truzone ok?

LOL that is exactly what i am using at the moment. I usually get the generic peroxide from Sallys, but got the Truzone stuff online and i am really liking it. Better bottles with flip-up caps so you can squeeze out the exact amount needed.
Remember with Matrix Light Master to drop a level of peroxide, it is strong stuff. You would probably be able to use 10 vol on your previously bleached areas, maybe 15, definitely no stronger than 20. I use 10 vol on my daughters dark blonde/light brown, she is slightly darker than your bleached ends.  20 vol on my own level 3 brown to get to palest yellow, it will go to a yellow/gold with 10 vol. With other bleaches i was struggling to get pale enough for pastels even with 30 vol. We both have very fine strands though, so you may not lighten as easily.
You could always strand test with the XXL kit and see how light it gets you, as your hair was virgin before the first application it should be OK condition wise.

Hmmm think I'll get 20 vol instead of 30 then. 
From what I've read, this Matrix stuff is both very good and very fast so I'll give it a blast with the 20vol (once I've faded this Rubine out a bit), maybe even do it section-by-section so I can control the process time better. 
If it doesn't get light enough in one go - which it might well do -  I'll dilute it down for a BB at a later date.

Thanks  🙂

I would try a test with 10 vol first. Pre lightened hair is more porous, I doubt you will need 20 vol.