I've recently developed some TriX in Acutol 1:9 that gave me some really nice crisp and VERY sharp grain. I was using a noctilux wide open and rated the TriX at 400 for some interior nighttime shots. I developed for 10 minutes at 70 degrees, and they turned out wonderfully. Since you shot at 1600, you could probably increase the time to 15 minutes or so and get acceptable results. The thing that I liked about Acutol over Rodinal was that it did not seem to increase the base fog as much as Rodinal tends to do when you use it at 1:25. The grain was very similar, however. If grain is what you want, then definitely stay away from solvent developers like ID-11, which contain sodium sulfite and will tend to reduce the grain.
That said, in a pinch you could dilute the ID-11 to 1:3 and develop for 30 minutes and get the grain you are looking for. Just be sure and put some empty reels in the tank so that you use an appropriate developer volume of at least 4 ounces of stock solution per roll of film.
I have not done that and it seems odd to me. TXP is totally different from TX and is not inteded for push processing, mainly not for more than two f-stops . However, Rodinal might perhaps do the job as you wish. Try 1+50 for 35 min @68°F and 1 minute agitation interval as a starting point.
Thilo, TXP actually pushes quite well. In this instance, I was presented with a fleeting opportunity in low light, and pushing was the only way to get the shot. Which was fine by me, because I wanted quite a lot of grain to suit the mood of the image.
I ended up usng ID-11 and it worked out OK. I duel selenium / sepia toned it. Will be printing more of them today and may throw a few into the gallery.
If you are looking to produce grain have you thought of trying Delta 3200 developed in Rodinal. The film can be pushed, I've taken it to 25,000 ISO, you may remember the image "New York Kiss" I posted a few months ago, the grain is sharp and depending on the speed used can vary in size. I find that rating it at 6400 developed in Rodinal 1 to 25 for 10 minutes gives me good negatives.
You may also wish to try Tri X developed in very dilute Rodinal say 1 to 200 or even 1 to 300 for something like 4 or 5 hours to increase the grain.
Rate the film at 1600 ISO and agitate for the first 5 minutes and leave the tank standing in a tray of water to hold the temperature at 20 degrees c. You will get excellent grain but you need to have a little contrast in the subject you shoot. I guess that you will be shooting portraits and will have some control over the lighting so that will not be a problem for you.