@lancmale, I've had a go a reading what's been posted to date but please excuse me if I've misunderstood anything.
So, the problem is you can't install from orig BD to external HDD?
You have mm and Gaia on Kmeaw's CFW3.55?
Does ripping to internal work?
Do you have a folder on your external thus: /GAMEZ ?
Are all your game rips going in there?
Do you have the latest mm? Well, the one before the lastest would be best IMHO - it posted - look for it - the earlier ones had issues copying/ripping.
Don't know about Gaia - haven't used it.
Look forward to your reply.
"We all agree your theory is crazy, but is it crazy enough?" - Neils Bohr