I miss the old Rifftrax Player... I have an installer for v1.1.1.5, which installs, but crashes every time I try to use it, and an installer for 1.9.8.8, which gives the well-known "server failure" error. So, despite how much I LOVED the Rifftrax player, I can't use it.
SO... most of the time, I just push my MP3 riff file into my little thumb-drive MP3 player, and watch the movie with my earbuds in. This works out reasonably well, though it's got a few major drawbacks.
Key to those is that it only works when I'm by myself. Otherwise, the other folks in the room think I'm insane when I laugh at strange points throughout the movie.

Now, I have a full, Win7-based HTPC where I'd prefer to do this (in my living room). I'd love to be able to play back the "Matrix" flicks with commentary for not just myself but for a group of my friends. I'd really, really like to be able to do this without having to install a second sound system in there, too. But I'm a bit stumped on how to do this.
Obviously, it's not an option going from my standard DVD or BD player, through my receiver, to my TV and speakers. It cannot "mix" media from various channels, and I'm not aware of any receiver or amplifier (at least any COMMERCIAL one) which can. Professional setups use separate mixer boards... no way I'm gonna do that just to listen to Riffs.
But on the HTPC, it ought to be possible to play back simultaneous soundstracks, shouldn't it? The "mixing" is all occurring inside the PC, in software, after all. This is really all the "Rifftrax player" did, when you get down to it... mixed them and kept them in sync. (Well, the "keeping in sync" is probably more complicated than I make it sound... but we all know that, so no need to belabor the point.)
Ideally, I'd think what we need is just a "wrapper" for something like VLC, where it opens two files at once (essentially two instances of VLC?) but consolidates them under one user interface. "Syncing" need not be a totally automatic issue... I'm fine with a set of buttons on the top saying "delay sound by 1 second" or so forth which I can hit to resync "manually" if things get out of whack. Fully-automatic syncing is wonderful, but just make the non-automatic version SIMPLE and I doubt many of us will complain!
Okay, so nothing like that exists yet, though. I'm not a coder, so I'm not really able to make it for myself (and I don't have the time or inclination to learn VLC's inner workings anyway).
SO... I'm curious what you guys are doing? Just doing what I do and using your "ipod-ish" device entirely separately? Trying to run two separate media players independently and syncing them manually on a PC? Rigging up a second sound system (say, an iPod dock?) to provide Riffs? What?