Thanks Larry!
The plot thickens ...

You stated "Your Fender PBass should (be) around 10K ohms ... This is considered “high” output impedance: between 6K to 10+ K ohms".

As shown in my OP, the input marked "Low" on the amp is shown as ... 65k ohms.
That figure is closer to my bass output than the input marked "High".
Why would I not plug the PBass into the "Low" input?

As you can tell, my lack of understanding on the subject, is underwhelming!

LLOYD S