Thanks everyone. Yes, I considered a prehardening bath for the reasons described here -- it would potentially protect the film from the beginning. I didn't want to add the complexity, though, if better tempered baths and a hardening fixer would solve my problem. I'll reconsider it though. I found a source for chrome alum, but I have no experience preparing chemicals from scratch like this.
I also considered Pyro, but I didn't want to start from scratch with a new developer (my repertory is already pretty broad!). I was also a bit put off by the statements about how the tanning/staining affects printing with filters. Right now I'm using XTOL and I like the results I get.
My current rinse method is a variation of Ilford's: Instead of 5+10+20, I'm using 1+1+5+5+10+10+15+15+20+20. Maybe that's excessive, but I wouldn't expect it to cause problems. Even so, I don't think it's thorough enough to rinse after a hardening fixer.
You are thinking...
If you are damaging emulsion it is most likely the acid stop, a pH swing and temperature change together is bad.
Hardening after stop may not help, you may need to prehardened.
Simpler not using acid stop and tempering.
Adox said for their Efke film
'We recommend the use of plain water to stop !'
I fair copy
Dump developer
Part fill tank with tempered water
Invert 20 times
Dump water
Pour in tempered fix: note I don't use acid fix either.
This is overkill but low risk at 68F should be ok much higher is more risk.
If you want archival 5,10, and 20 tempered water is ok, if you use hardner you need
Fix,
Rinse,
HCA
5,10,20,&40
It is best if you invert wait for water to flow then upright tank wait for water to flow.
It is the flow that refreshes the water film over the emulsion. Which would otherwise be static. You don't need to waste more water.
The HCA counters the hardening process.
Good luck.