Well, we're back from the vet - I think this was Dr. Munn's day off (or surgery day?), so it was incredibly sweet that he was able to take Mr. Honeycomb in.
It's a bad URI - but just to be sure, he listened carefully to the lungs, probed for any type of tumor, and listened to the heart. The heart was the only issue he couldn't be sure about, largely because the noise from Mr. H's lungs was so loud it would have been impossible to detect a murmur. The vet tech was totally charmed by Mr. Honeycomb, and so was Dr. Munn - even when he feels terrible, he loves hamming it up!
So, bay/doxy for a month or thereabouts, metacam and theophylline (oral bronchodilator) indefinitely, and Ensure and baby cereal for at least a few days (to make sure he gets enough food, he lost 30ish grams since December). I gave him his first dose of all of them as soon as I got home, and I think he's sounding better (at least the noise he's making isn't giving me heart attacks like it did all last night).
He's going to stay up in my room because I have a humidifier up there, and he'll have regular one-on-one visits with the girls. I'm sorry if I'm rambling, I'm severely sleep deprived - I kept waking up whenever he'd honk particularly loudly (or sneeze or anything) - I gave up on sleep around 5AM, which for me is equivalent to pulling an all-nighter. >.<
Edit: Unless there's a heart murmur or something that shows up once the URI is cleared, it isn't likely CHF, as he's pink in all his extremities.