thank you very much.
I super appreciate your replies Qexl and Gilles. 

Not 100% clear on the issue - is the issue that you're trying to arm all 20 tracks at once and it's not working?
I think the only way to do this in Logic is to select all the audio channels, assign a different input to each, create a group, and select "record" in the group settings.

I just did it, it seems to work consistently, and midi records. I didn't do 20 tracks, only 8 but it worked as expected. Here also you get more info-https://www.garagebandonpc.org/

thank you very much Qexl.

I am very new to Mac.

I don't see Pianoteq showing in the AU list.
do I have to do something to make it appear in the list?

Here is some general indications (on Mojave):

Starting with an empty project, select a software instrument track to create. By default it shows the embedded electric piano. In the Track panel you should see a "Modules" menu near the bottom. Click on that. When it opens, click on the up/down arrows on the blue name (should be "Vintage Electric Piano") and you will get a menu for the AU instruments, both from Apple and Modartt.

Not very easy to find I agree...

But first! - have you torn'dit orf, then torn'dit barke orn again? - that's a helpful thing sometimes after installing some software with plugins, no matter the OS - it shouldn't be a thing - but can be joost da ting.

In MacOS X 10.7 or higher, think it should handle Piantoeq with AU (from Pianoteq FAQ).

Here's a GB tutorial on getting AU working within GB

And, if that's not the fix you need.. these 2 links have videos which i hope cover your issue.

I found this tutorial for plugins with GB.. hope it helps you! I could try typing a short-cut version out - but since I don't run Mac, it's prbably more useful to read that site.

I am guessing someone else with a Mac can correct if these turn out wrong or outdated? Hope that gets it working.

Cheers chas.

I am very new to Mac.

I don't see Pianoteq showing in the AU list.
do I have to do something to make it appear in the list?

Some confusion might arise because of terminology, for example, "Audio Units" (AU instead of VST type instrument tech) are sometimes mixed up with some classical idea of "audio instruments"?

To anyone new to audio, it's all Martian - but Pianoteq can be used in a DAW as a VST plugin.. but in the Mac world, it may be loaded as an AU (Audio Unit) - but that's different to an audio wave file, or an Aussie thing

The next rabbit hole will appear, in ten minutes, don't be late!

Cheers, hope that helps you work out how to get it doing what you need.

Hi!
If you with audio track mean a wav file, then you can export your recording as a wav (uncompressed 24 bit) and the drag it back to Garageband which create a new track with the recording as an audiofile ( wav). Don’t know if this is what you need? Good luck!

thank you very much.

I want to record as Audio wav files directly on to the GarageBand track.
I do it in Reaper, and it works very good.
in Reaper, I load Pianoteq as an FX VST plugin.

in GarageBand, it will let me load Pianoteq in a Software Instrument Track. but it only records MIDI.

Audio Tracks do not show Pianoteq.
is that just the way it  is in GarageBand?

thank you for any help,   
Charlie