I don't know if 2" PVC will be good enough...I guess it depends on the amount of gear you have or will have.
If I grab a handful of cable that I currently have coming out of the back of racks...it would choke a couple of 2" pipes and then some....but I also use a lot of individual runs.
Ideally, and what I'm going with in my new studio build...will be 48-channel Mogami for running between the gear and the bays, which is about 1 1/4" in diameter. For any wall plates at a distance, where I would go through the walls, I'll probably get some smaller, 24-channel cable.
I'm not sure what type of cable is used on DB-25's....I mean, there are probably many brands/types out there, so which are you referring to?
For in-wall, the best would be the type that has both braid and foil shielding...it's a bit stiffer, but the foil is 100% shielding, and since it won't be moved around in the wall the stiffness is not a problem or the possibility that the foil will crack from movement...but then, you still have the braid underneath anyway.
For cable that gets moved around, you want just the braided shield, and really good quality outer layer that can take the abuse.
For me...Mogami, Gepco, Belden...those are the top choices...though lately I've been using a good deal of Kirlin cables for guitars/instrument stuff, and it's quite good. Kirlin is a newer company, I think out of China, but they're making a quality product. No idea if they make multi-channel audio cables in bulk...etc.
I already have a good deal of brand new Mogami 48-channel, so that's what I will use for most of the stuff except any in-wall runs because I only have pieces that are like 30'-40' each, which is enough for the racks/bays/etc...but maybe not long enough for a wrap-around wall run.
I got the Mogami for free off of a huge wooden spool. It was bought for a big theatre installation, and then never used. I was able to unspool several 30'-40' pieces and cut them, because there was no way I could take the whole spool...I would have needed a forklift, but if I had one, I would have take it all!