I understand what you are saying and I understand your goal, however, I think that whether you decide to notch or discriminate, you will get the same result. Notch is an expanded function of discrimination and as far as I know, notch works in the same way as discrimination. This means that if you notch say 0-30, it is the same thing as discriminating 0-30.
The reason you lose depth with increased discrimination is because the processor is working harder on discriminating targets and ground noise rather than working on identifying targets you "want."
By lowering discrimination, you hear more in the ground, but the computer doesn't need to work as hard at filtering out the noise so you are able gain some extra depth.
Long story short, the best way to run higher disc and still get the maximum depth, is to discriminate with audio adjustments as you are already doing. If you want a silent hunt with a lot of disc and notch, you are going to lose a little depth.
If you are in an extremely noisy area and want some silence, I would recommend running higher disc and sacrificing a little depth. From what I have seen in depth loss, you will still hit on most targets and might just miss the targets that are on the edge of detection anyway.
Let us know what ends up working for you as I know your not the only one with this question.
Hope this helped,
-Marc