Thanks for your advice.
I can't give you a purely technical response as I am not an Engineer. I do it by feel and looking at the waterfall and listening to the noise floor. I adjust the level down as you do until the weaker signals pop out of the noise floor. If I find that I am not copying completely I then raise the level just a bit to see if there is improvement.
As I mostly do digital (PSK mostly) I have found the settings to be easier than with voice. I lower the AGC until the signals show (based on the weaker ones) with minimal background. Then I raise it a bit to give me some headroom and use the DAX RX gain to make fine adjustments.
My 2 cents...
Here's how I adjust my AGC, DSP, Preamp and cw filters, for weak signal cw on my F6300. This is real world adjustment.....find yourself a weak signal beacon on 10M, one where you can see the signal on your waterfall but just barely hear it in and out of the noise or see it on the panadapter. I usually start with a "FAST" setting, then adjust your AGC and DSP for best signal-to-noise. This may take a few minutes to do, considering possible QSB.
I would also like to mention that in my opinion there is still too much noise and ringing when using
the 100, 50hz filter, and narrower settings. I've said this before and hope it is being worked on.
I am a CW operator and here is what I do.
1. I always run headphones. Use a good pair of headphones that do not ring at narrow filter settings. Some headphones will keep resonating or ringing.Speakers tend to cause sound reflections and ringing at the narrow filter settings.
2. I run a higher cw pitch setting 700hz. The human ear is non-linear and can resolve tone frequencies better at higher settings. I can not hear the difference between 500 and 510 hz but I can hear the difference between 700 and 710 hz fine. Being a musician helps!
3. I always run with the 50 hz filter on CW. Improves the signal to noise and then you do not need the NR, NB, APF. CW is a single tone, usually depending on the other guys transmitter and a single tone will easily fit in the 50 hz window.
4. Now to answer your question. Crank the AGC T all the way to the right. Set audio level slightly higher than you normally use. Now crank the AGC T back until the other station sounds good.
I find the control I am always adjusting is the AGC T, not the volume control when I have it set correctly.
Oh, i always run Fast AGC.
Just my thoughts, others may have different approaches. Treat the AGC T like it was an RF gain control on an old fashioned receiver.