You have the right machine, coffee, and grinder for making espresso better than the best espresso you have tasted in any cafe. That is my opinion based on my experience. So how to fix this? Grind finer. Try WDT to determine if that helps, however I don't think it is necessary with the grinder you are using. Likewise for pre-infusion, which might make a subtle but negligible taste difference, should not be necessary to perfect your espresso brew.
I use either a Pullman big-step tamper or Mahlgut Buzzer Palm level tamper. Both of these have a sharp edge and are the exact same diameter which fit just right into the VST baskets, which you mentioned is equivalent to what you have. Ensure your tamps are dead nuts level. If you have a very short brew time, grind finer. If you have channeling, then try WDT (paperclip works fine). I bought some plastic cups in the supermarket which work well for funneling into my pf.
The only other thing I can think of is the coffee. If it is stale, then replace with some fresh coffee.