Assuming the enhancement indicates CNS inflammation, then given the lymphadenopathy and time of year of onset and aggravation, my suspicion would be a Shao Yang disharmony - your favourite new diagnosis!
To confirm, you'd want to see the pulse improve with massage or acupuncture to key GB points like GB 20 and GB 34 for example. Try the latter first. If the pulse improves, for sure that is what is going on.
In terms of treatment, you'd need Minor Bupleurum on board. That should resolve the inflammation. I assume the pred is there to address the enhancement? If so, the XCHT should do a better job of resolving it, making it less necessary.
Tian Ma Gou Teng Yin can be used with XCHT to control seizure tendencies.
The longer he is on Phenobarb, the harder it is to discontinue without triggering seizures. It's also likely the drug that is sedating him. Perhaps after robust herb dosing (if you can accomplish that) for a week or so, try lowering the phenobarb. Not too much though. Just a 15 or 20% reduction, if you can swing it. If that produces no seizures and the cat improves, then look at lowering it again if you like.
Once you're at that point, you can start looking at discarding drugs. The probiotic is a good idea in Shao Yang cases, but the clindamycin (for the lymphadenopathy?) and the pred will hopefully be expendable if you can dose consistently with XCHT. Check the acupuncture points to see if it's likely to help