I'm not sure what exactly fixed it, but I spent a few hours this afternoon downloading Blackhole and trying to set up an alternative way to use it to access the Pianoteq audio buffer. This involved a lot of setting up aggregate and multi-output devices in Apple's Audio MIDI Setup utility. None of that worked for what I needed, but in the end, when I went back to check on `auval` again, I'm finally seeing that the Modartt entries are recognized/registered properly:

$ auval -a | grep aumu
aumu Ot2q Mdrt  -  Modartt: Organteq 2
aumu Pt9q Mdrt  -  Modartt: Pianoteq 9

In all that messing around, something fixed it (by updating a cache somewhere maybe?) but I can't be sure what it was.

To be specific:
- system-level Audio Unit validation fails
- the auval command line tool cannot validate the components

Some observations towards debugging this:
- Running `auval -a | grep -i mdrt` returns no results, so it seems the OS is not seeing any Modartt components at all.
- Logic Pro can still load and use Pianoteq and Organteq
- The component files exist in the correct locations:
    - /Library/Audio/Plug-Ins/Components/Pianoteq 9.component
    - /Library/Audio/Plug-Ins/Components/Organteq 2.component
- Running `auval -v aumu Pt9q Mdrt` produces:

ERROR: Cannot get Component's Name strings
ERROR: Error from retrieving Component Version: -50
FATAL ERROR: didn't find the component

My best guess is that this is a compatibility issue with macOS 26's Audio Unit registration or discovery mechanism. The components appear to be properly signed and Logic Pro can still use them, but they're not being registered with the system's Audio Unit component registry.

Thanks in advance if anyone knows a fix for this or can suggest an alternative way to access the audio buffer.