Let me see if I understand you...
First, when I say 'real time' I mean the transport has to be moving (either play or record).
When you are playing the Tascam from any two tracks you are sending song data in digital, serialized (spdif) data format to your computer to any sound card that will receive spdif data and recording it in some kind of package like Pro Tools.
When you are recording with the Tascam transport moving you are receiving spdif data as the song is playing on the computer from a package like Pro Tools.
Just to be clear, you cannot use both send and receive simultaneously on the Tascam. The reason is that the Tascam will not let you do that - you must do one or the other.
When you write "stereo bus (realltime) effect" I think you may be thinking that you can send from two channels on the Tascam and simultaneously record (receive) on two other channels on the Tascam - can't do that (if that is what you are saying?). If you could do this it would be more like an external, effects send and receive loop.
In any case, are you saying that you can send and then receive your master (sub-master for Tascam) mix down? And if so, you could process the master on your computer and then send it back to your Tascam running in record mode? I guess this would allow you to process the master (or any two tracks in theory). If you kept your raw tracks on the computer you would always have a golden copy to go back to. A couple issues with this would be: 1) the sync would be hard to do for punch in and out (and therefore editing; you can also get unwanted pops this way) - it seems like you would have to send the whole processed track back from beginning to end 2) you would have to do this for every set of two tracks, including master, that you want to process 3) there would be a lot of track juggling on the Tascam which you could do with virtual tracks I suppose OR you could just keep the golden raw tracks and any processed tracks you want to save on your computer and simply record over the corresponding, previous tracks (do all the track juggling on the computer) 3) it seems to me that rather than go through all that...just get all the raw tracks in your computer and do the rest of your mixing and processing on the computer. There are a lot of great packages on the computer that would handle automated mixing, processing and mastering without ever going back to the Tascam.
As a side, I really like the spdif but for different reasons. With spdif you can get digitally clean tracks back and forth to your computer without going through the digital to analog and analog to digital conversions (and thereby introducing noise). The more you can stay in digital land the more pristine your final mix is going to be.
Oh, also...this is why I have always like the forum - where else can you find folks that specifically discuss recording and the Tascam like this?