Questions for the Knowledgeable - APx555, Analog Filtering, and Test Signals

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I had some questions RE: the APx555, and I figured I'd ask the knowledgeable membership here.

So, I understand it uses a (variable?) analog notch filter (plus preamp, splitting signal, second ADC, etc.) before the ADC, in order to cut out the test tone frequency and take measurements with ADC distortion < -150 dB. I'm curious about the following:

1. How many simultaneous tones can be handled? Is it only a single notch filter, to handle one tone at a time, and after that you're limited to the ADC's distortion?
2. What about signal generation? Do they implement a similar solution after the DAC with a band-pass filter to cut out any DAC distortion of the test signal? Edit: Never mind, I've found out the AP has an analog signal generator as well.

Thanks in advance to any APx555 owners/connoisseurs who can answer.

Edit: if anyone else is curious and finds this, I ended up finding a decent rundown at the below link.

https://archimago.blogspot.com/2020/07/pictures-audio-precision-apx555-b.html