Wow!
I've never heard of TKD Super D's,... ok so I just Google'd it and it seems to be a Europe-only product.
TDK 1997-2001 EUR
I think you lucked out on that purchase! It's a little older tape but not ancient. You are set!
The 424mkIII is limited to 4 tape tracks, only. Channels 5/6/7/8 are mixer channels only with no corresponding tape track.
Channels 5 & 6 are full mixer channels with EQ and AUX Sends, and may be routed to Buss L or Buss R to be recorded to any of the 4 tape tracks. Additionally, Channels 5 & 6 may "borrow" the inputs from either 1/3 or 2/4, respectively. This enables you to use (borrow) the XLR inputs from Channels 1-4, while simultaneously using Channels 1-4 sourced to "Tape" for mixdown. This could be handy if you want to add live input parts at mixdown time using the XLR mic inputs. 5 and 6 also have their own 1/4" input jacks as a baseline.
Channels 7 & 8 are either "mono" when you're using Input 7 alone, or "stereo linked pair" when Inputs 7 & 8 are used simultaneously, however it's only "Level" control and no other knobs & not including a full mixer strip. 7/8 may be routed to the L/R Busses and recorded to tape, "Off", or directly into the Monitor section only (bypassing the buss and tape sections).
All the Channels 1-8 may be mixed and routed to Buss L/R and to tape, for big-setup recordings, such as a live ensemble or drum kit. Channels 1-4 also correspond with the "Direct" recording feature, where Channels 1-4 route directly to it's numerically corresponding tape track. 5/6/7/8 don't have Direct mode capablily at all, but they route to the Busses L/R, if you need them they are there.
For "bouncing",... I won't get long winded here until you've gotten your feet wet on the 424mkIII, BUT you may record your mixes in stereo to the DP02, create a stereo master track on the DP02, and record the master track back into two tracks on the 424mkIII, to add 2 more tracks on tape. In fact, if you're careful with setting levels, you may skip the "Master" track step entrely, and record your bounce to/from the DP02. This preserves your primary tracks in the bouncing process, and is known as an "external" bounce.
The other "bounce" technique is an internal mix of tracks onboard the 424mkIII where tape/pgm tracks subsequently gets taped to an open tape track, but that destroys your original tape tracks in the process. There are descriptions of this process you can find, so I won't detail it exactly, but very carefully you can get acceptable results from this method, that may pack up to 10 "parts" onto 4 "tracks", which includes adding a live part to the bounce during this process.
In general, I think it's accepted that any track-bounce operation will diminish fidelity somewhat, and maybe an external bounce to a lesser extent than an internal bounce, but both methods bear out some experimentation. However, where an exteral bounce shines is that it preserves your primary tracks, and an internal bounce does not. Both methods, if used and with great care, can yield acceptable sound quality. However, the bounced track parts remain locked in balance with each other on each bounced track, which is a consideration.
I may go off topic here, but in general I think if your 4-tracking scopes a lot of bouncing regularly, you're probably better off with an 8-track instead. Fidelity wise, I would always consider an 8-track cassette such as the 488mkII superior to a 4-track cassette using a lot of bouncing. However, you kind of cut your teeth on the 4-track, use bouncing if necessary, and move up when you can afford to upgrade. Nonetheless, you have the DP02 if you want to dump your 4-track stereo mixes to that and add more tracks, it's all good.
The 424mkIII manual is pretty good, in general. I'm not too keen on the step-by-step tutorial, but it suffices for the novice.
Sorry for the long post.
