Tascam, Fostex, Analog or Digital?
The X-12 is functional, but the 424mkIII is a fair upgrade to the Fostex, I'm pretty sure you recognize that. It would be a good step up, but keep in mind the Fostex system is Dolby NR and the Tascam is Dbx noise reduction, which are not compatible. You'd probably need to keep your Fostex around to play your older tapes back properly, or just use the Tascam to play them back, with the dbx noise reduction switched off. This, of course, would invite unwanted hiss back into the mix.
As to whether you should skip the analog route, and go digital,... well,... that's a very personal choice, of course. IMO, the analog Portastudio still gives many high end features that the digital 4-trackers cannot touch. Likewise, the digital formats give capabilities that cannot be rivalled by analog. I believe the analog Portastudio gives full features, ease of use, and pleasant sound quality, while the digital's offer smaller size, virtual tracks, and EDITING capability that's way beyond what's feasible with cassette.
F/I, the 424mkIII gives an 8 input/6-full-channel relatively high end mixer, and lots of digital 4-trackers offer only 2 inputs.
There may be other differences that I've glossed over. Shop features carefully, when you're considering a recording upgrade.
OKAY, having said that, I know it's perfectly feasible to pick up a USED Tascam 388, for relatively the same price as a NEW 424mkIII, which is a HUGE UPGRADE over 4-track cassette. The Tascam 388 is an analog 8-track, Portastudio format, all-in-one 8-tracker, that runs on 7" reels of 1/4" tape. The 388 also sports a VERY high end 8x8x2 built-in mixer, rivalled by none in it's class. THIS 388 1/4"-8-track format is worlds ahead of any cassette 4-tracker, or digital 4-tracker out there.
I've gotten a 388 used for less than a 424mkIII new, and so have people that I know. The 388 was a pro-format machine for the small pro studio, post-edit and sound-for-film studio, when it was first introduced, and many can be found out on Ebay in like-new condition, for about 10c on the dollar. The 388 was over $3000 when new, and sells currently for ~$300-$550, depending on the day.
I just visited one of our newest Newbies, who scored himself a LIKE-NEW, almost-no-use Tascam 388, for $300, which IMO was a phenomenal deal & value. I checked it out myself, in person, and it is indeed LIKE NEW.
Search this site and Ebay for more info on the Tascam 388. I think it's the best Portastudio format machine ever concieved or built.
As for what is the future of regular cassettes for mixdown purposes? It's obviously on the decline, but I don't think it will disappear entirely.
In the end, no matter what the audio market does, at large, you just have to find a recorder that works for you, and go with it. Every format has it's heyday and it's decline in the marketplace. The market is fickled, at best, when it comes to things like this. JUST when you think the market has dried up, gone away, or the way of the dinosaur, a NEW RETRO market may pop up, with just as much vigor as the original. Look at the "toob-gear" market, and all these "boutique" analog preamps that have become an industry, when "Digi-mal" was thought to be the dominant technology.
The market is fickled. Go for what pleases you best.
I recommend the Tascam 388 as the logical step up from the common analog cassette 4-tracker.
Tascam Portastudios are better than Fostex porta's, almost without exception.
That's MO, and YMMV.
