I hesitated to return to this thread; now I'm glad I did.

I went to look and meet all your cats, what a lovely clowder you have!

I also did some checking on FIV online -- as I have one FIV+ boy, never hurts to recheck stuff. So, those things that you listed from th cat medicine book, I found here too:
http://www.animalhealthchannel.com/fiv/symptoms.shtml

I didn't remember that FIV progresses in stages. This is the bit I remembered:
FIV & Opportunistic Infections

Opportunistic infections are the major cause of death in FIV-positive cats. They usually develop in the skin and the gastrointestinal tract. Some common symptoms are poor coat condition, persistent fever, and loss of appetite. Other symptoms and conditions include the following:

And it is under that section that they list the anemia, weight loss, and other things you had listed.

So, if you can treat each symptom, that should help.

The reason I was afraid to come back is, as I thought about how you and Laura described him, 5 pounds and so thin, I sort of ended up leaning the other way. I'm glad you are going to push forward and give another try!

Those 2 meds should cover infections. I wonder about something for the anemia? That makes a person feel tired and sluggish; if that is addressed, it may help him feel better.

Prayers for Gabby, and for you, from RI.