Why are the Infinity IRS, Reference 1b, Beta ect speakers passive on the mids and highs?

The pots were poor.

Pots are always a problem when old in any speaker, you replace the pots with appropriate resistor L pad power resistors of the same values for your preferred setting.

Cheers George

I am learning here. Timlub, it sounds like you have experience on the RS1B. Is there anywhere I can get specifics on what to do to improve the RS1b. What made me start the thread was an experiment I did with the RS1B's I have. I disconnected the crossover and tri-amped the system. I know a lot changed because all of the EMIM's went to a midrange whereas passively 6 are 150-700 and 1 is 700-3500 but I did not like the sound as a simple 3 way. I have another system where I have 10 EMIM's and a ribbon tweeter from a magnepan 20.7 where the tri amp works pretty well but falls short in some ways to the RS1B. I am trying to figure it out.
Marc

Partroysound
When you tri amped them what crossover points did you use?

I have not triamped these, I've never owned them.  I worked for Marcof/SpeakerCraft, we did alot of custom work and I got these to work on years later because of my time there. I worked on the crossovers only... Measured each ribbons output individually, then customized the pads within the crossover.  So without having complete driver measurements, that's why the basic design wasn't changed... better caps and coil or 2 and hand matched pads. 
For me, as long as your amps can handle driving ribbons (some cannot) and you have a very good crossover, this is a no brainer. 
It will take a bit to get these matched, but I would expect excellent results. 

partroysound: If your m/t panel wings move relative to the wings base as much as mine did, I would definitely attach a length of hardwood (or metal rod, like the Quad 2805 and 2905) to the backside of the m/t panel wing near its top, the other end secured to the wings base. A small hinge at each end would work fine. Those wood screws "securing" the wing to its base plate are woefully insufficient for the job. Then, an outrigger fitted to the bottom of the wings base plate will create a deeper footprint (the base plate is too shallow to provide front-to-back stability), locking the EMIM and EMIT drivers in space by preventing fore-and-aft swaying, for increased resolution and transparency. The bass enclosure can also use a wider footprint, again via an outrigger. These measures address and remedy the structural weaknesses of the RS-1b. The drivers and their filters is a whole 'nother matter.