Your bass response issues being resolved by the digital makes the tt setup the obvious culprit. Attending to other issues will only delay your getting the tt setup right.
The wall shelf will make little or no difference in the bass, I've tried both wall and floor setups, the wall setup is much better overall in other sonic aspects. I suspect the fact your setup sits on a cement slab will make even less difference vs. the wall setup. I highly doubt it is your tt isolation.
I had the Pro-ject Tube box in a former tt setup, I doubt that is the culprit. I actually found it to be somewhat dark sounding in that setup, it probably doesn't have the bass impact of the highest quality phono stages.
You may also want to try an armwand with the standard Discovery cable, more even tonal balance in my setup. My only problem with that cable is it seemed a little closed in on top, it also doesn't have the resolution, air and spaciousness of the Valhalla cable. I also think it may be worth considering a custom wired armwand with Cardas, Purist or some other wiring, this could make a worthwhile difference. The Purist will definitely take the bass up a notch.
It would also be enlightening to audition a higher end phono stage, I've tried this path with no success to this point. Based on my experience you may have a long road to go in getting the VPI to sound the way you want, on the other hand, perhaps the next upgrade and/or tweak could solve the problem. Kind of exasperating not knowing how far or close one can be to solving audio problems.
The wall shelf will make little or no difference in the bass, I've tried both wall and floor setups, the wall setup is much better overall in other sonic aspects. I suspect the fact your setup sits on a cement slab will make even less difference vs. the wall setup. I highly doubt it is your tt isolation.
I had the Pro-ject Tube box in a former tt setup, I doubt that is the culprit. I actually found it to be somewhat dark sounding in that setup, it probably doesn't have the bass impact of the highest quality phono stages.
You may also want to try an armwand with the standard Discovery cable, more even tonal balance in my setup. My only problem with that cable is it seemed a little closed in on top, it also doesn't have the resolution, air and spaciousness of the Valhalla cable. I also think it may be worth considering a custom wired armwand with Cardas, Purist or some other wiring, this could make a worthwhile difference. The Purist will definitely take the bass up a notch.
It would also be enlightening to audition a higher end phono stage, I've tried this path with no success to this point. Based on my experience you may have a long road to go in getting the VPI to sound the way you want, on the other hand, perhaps the next upgrade and/or tweak could solve the problem. Kind of exasperating not knowing how far or close one can be to solving audio problems.