Apologies for the late reply-- I've been off HF for a while. I don't believe they are available anymore, but beyerdynamic made clear gel pads that fit the T5p (an example from a closed classified is here, if it helps). They can still be found used from time to time, and if you come across a pair, I'd still recommend them-- best pads I've heard on the T5p thus far (from an admittedly small sample set, but nonetheless). And yes, I've tried the stock pads (naturally) and the J$ pads in addition to the gels. I'm having trouble finding my notes on the differences (I've changed computers since I wrote them), but as I recall the gels are the least comfortable of the three by a small margin and the ugliest of the three by a mile, but they isolate better and improve the bass response (very brief mention here). If I can find my original notes, I'll try to copy them here.
If you have any other questions, please let me know and I'll do my best to answer them. Overall, I think they are absolutely worth the $30-or-so that they typically show up for used. Hope this was at least somewhat helpful!
And if you have a set of T5ps, I'm sure I wouldn't be the only one who would love to hear your thoughts on them!!
Edit: Missed your question about other mods. The mod most commonly referenced with these is switching to a balanced cable, which at least three companies (BTG-Audio, Moon Audio, and Jaben-- but Jaben won't do the mod by itself, you have to buy new cans fully modded) offer. The consensus, such as it is, appears to be universally positive, and I plan on having BTG mod mine as well at some point. There might be other mods, but I'm either unaware of them or unable to recall them at the moment ;).
I was actually thinking of trying some Alpha Pads! LOL!
Will order at least 1 pair of those this week for another set I have but will try and see if they fit.
I did speak a bit about them on my Alpha Dogs review:
Also got some Beyerdynamic T5p with Blue Dragon cables, bought used. The only other Beyer I had was the DT770 Pro 80s which are basshead preferred and they don't sound anything alike. Anyway, I have to say that the T5p's are "Ok". Their highlight is definitely their mids, very clear, forward and just excellent. Soundstage and imaging are very good as well but their highs are a bit too much sometimes (maybe too revealing to my tastes or maybe they are too peaky?). Bass is actually quite anemic (surprising since the DT770s were so powerful) but what it shows it's good quality. These are very comfortable as well, good isolation and no leakage.
Bass quantity: SRH1540 --> Alpha Dogs --> Beyer T5p
Bass quality: Alpha Dogs --> Beyer T5p --> SRH1540
Mids presentation: Beyer T5p --> Alpha Dogs --> SRH1540
Soundstage/imaging: Beyer T5p --> Alpha Dogs == SRH1540
Highs: Alpha Dogs --> SRH1540 --> Beyer T5p
Sound Isolation/Leakage: Alpha Dogs --> Beyer T5p --> SRH1540
Fun Factor: SRH1540 --> Alpha Dogs --> Beyer T5p
Price: Alpha Dogs == SRH1540 --> Beyer T5p
So, as mentioned, mine already have Blue Dragon cables with them, but I think I'm going to do something crazy soon (once I sell a few things...). I contacted Martin (Martin Custom Audio) and I think I'm going to have a Woodie T5p soon! LOL Yeah I know... ;)
Oh, and thanks for the response! ;-)