I have a passive Venturi air system.. there is no blower, there is a air intake pipe a few feet from the Spa that feeds the air side of the Venturi nozzles. I think that is how your lower spa jets are constructed.
So, Yeah, I understand what the PB did to your Spa and what you are trying to accomplish. The proper fix is to tear it up and plumb air lines to the nozzles per the instruction that
@mas985 posted. And I totally get that you are looking for a work around given that there is no way the PB will cover it. So given that you have 2" plumbing which is not really big enough pipe to support 8 jets regardless of the pump (also per Mark). I thought I would suggest reducing the number of Jets. It would be easy to test. plug every other Jet and see if you get sufficient pressure on the others with the equipment you currently have. just an idea.