I am still trying to comprehend Opus Clavicembalisticum. I can't pick out every fugue subject yet. I also can't hear where each of the 49 and 84 variations start and end.

Actually, I am starting to comprehend the first fugue, the first 8 measures.
Well first of all I'd like to offer my congratulations to you for trying to familiarize this piece, instead of immediately dissmissing it like most people do.
It's important to understand that you won't have much to work with in the two available recordings of Opus clavicembalisticum. Well the main problem with Ogdon's recording is the pianists mental state at the time. I guess he just wasn't up to something so intellectually challenging in his condition. There are many peculiarities in his performance, such as the gross exaggeration of dynamics and in some places the complete opposite dynamics of what is written in the score. I recall one particular variation marked mp which Ogdon played as forte if not fortissimo. There are many important thematic references that Ogdon missed as well, for example, the return of the subject of the first fugue in pages 248-250 of the Coda-stretta (the chordal section). I didn't quite hear the subjects properly in the martellato at the top of page 250 either. The big problem is the time Ogdon takes though. An hour over the intended time, and many movements as played by Ogdon are either painfully slow, or too fast to make sense out of at all. The movements falling into the former, would be the passacaglia, the last two fugues, and the coda-stretta, the latter, the Fantasia, Cadenza I (which could actually go in both categories, the second section is far too slow, while the first is too fast)
It's unfortunately very difficult to appreciate or even comprehend Opus Clavicembalisticum for what it is with the two available recordings, which often miss the point of the music entirely. It would be easier to study the score while listening to the Ogdon. Avoid the Madge at all costs! When we finally have Mr. Powell's recording, I'm sure OC will make a lot more sense to us than it currently does.
I still have to figure out what he does with the themes in the introito and choral prelude. I am going to dissect all themes, put them in Finale and play/sing them. Actually, the first fugue is almost starting to bring tears to my eyes. And the last time that happened is quite some time ago.
The Introito is basically a short movement in which Sorabji exposes the main themes of the work. We hear the first at the beginning. the MOTTO. Several other themes come in throughout the movement. After this the Preludio-corale is basically variations on these theme. They pop up literally everywhere in this movement. The fugue is very beautiful, some of the textures in there are wonderful. The rest of the fugue after the first 8 measures is very interesting. After a few pages, Sorabji transforms the subject into inversus, cancrizans and cancrizans inversus, which are used for a while in counterpoint with other forms of the subject. The inversus is a reversal of the intervals as you may know, so a tone ascending becomes a tone descending. Cancrizans: the subject played backwards, and the last is the inversion played backwards. You will probably have noticed that Sorabji always swells up the fugues to huge textures in the last few pages.
I don't see how I can delve into something new that fast. I do need the sheet music of the 4th sonata otherwise it's impossible to listen to Sorabji.
I agree. It's a huge amount of music to take in one go without the score, and unfamiliar with it.
About Sorabji, the national radio broadcasted Sorabji's 5th piano concerto and one of his symphonies a year ago, along with some of his songs for soprano. They had 3 days dedicated to him. Maybe I should try to contact them if they still have the material achived.
It would be interesting if you could obtain the recordings. Maybe there's a way to get the first ever performance of OC by Madge in the Netherlands, which I've heard is far better than his horrendous Chicago performance.