[quote]that "guy" is a moron. [/quote]
That guy is me. :) Do I qualify as having had enough experience in this particular arena? :)
Minidisc or DAT or PC-based recording without a DI box from any mixer gives unreliable results - and especially noticeable on a DJM600 because of the way it compresses the sound when compared to the Allen & Heath range. The signal can often be too hot, even with your recording levels riiiiiight down. A very low volume, highly distorted recording is not what you want. In fact, you can hear a minimised example of this in my recording of Zabiela from 2003 at Lot 33 - the recording levels were just above silent, and there's still distortion when the bass kicks in some areas of the set.
Adding to the pressure are the effects built-in on the 600, plus the fact that James uses a EFX500 or EFX1000; especially flange. FYI - the 1000 is better with level management than the 500 is.. and I feel the NYE set I recorded bears this out.
By putting the DI box in between the mixer and your recording equipment, you give yourself complete control over the levels. A DJ can push absolutely everything to the max, and your DI box will act as a buffer. This is the same reason high-level DAT field equipment (Tascam DAP1 for example) has a "clip pad" built-in. Not to mention a DI box gives you added control over lifting an earth when required, meaning you don't need to apply filters afterwards and muddy up your sound.
Auto-level control on a Minidisc (or DAT for that matter) will do jack shit all if the rec-out is being driven to the brink in all areas as it often is in a peak-time club environment.
(For the record, a maxing of the incoming signal way beyond your device's capabilities is unlikely to do any damage to it... it's more a matter of 'blowing away' the recording for any useful purpose. Been there, done that plenty of times.)
PS: you can pick up a stereo DI box by Behringer for bugger all. Look for a DI20 and it will cost you about US$20. You'll also need some cabling made up (unless you've got an XLR to minijack lying around) but hey.. if you're serious about it, go for it. I did.