I'm so sorry that he still has blood in the urine.
But it sounds like your visit perked him up, and it's good news that he's alert and eating.
I am not an expert, but looking at those labs, I am even more puzzled by the infectious anemia diagnosis. True, his RBC count is low, but his HCT, while on the lower end of normal, is still in normal range. Kitties with HCT under 30 are diagnosed as mildly anemic.
The blood chemistry is very limited, but the kidneys are fine. I'm still wondering what that other med, the nefrotec, was for. Are you still giving it?
Does the new vet agree with the diagnosis of infectious anemia? Does he/she have any ideas of what might be going on if it's not stones?
Essentially, the vet needs to know what's going on in order to treat it effectively, so I think it would be worth it to go all out to try to get a firm diagnosis.
If this were my kitty, I would ask the vet to repeat bloodwork, but do a full blood chemistry, and a CBC with differential, and a urinalysis. I would also ask the vet whether a urine culture & sensitivity test, an ultrasound, and/or a PCR panel would be helpful in trying to diagnose the issue.
Oh, do you have the results of the urinalysis as well?
Is it one more day in the hospital? I hope you'll be able to visit. Don't forget to bring some clothing from home so he can be reassured while he's there!