Okay Big E...you are in luck!!!
JL Cooper makes a little box called the Data Sync 2. Less the US$200, and you may find a used one cheaper yet.
It has ADAT sync in, and will provide SMPTE and MTC out, which is derived from the ADAT sync in, which obviously comes from the ADAT. The outputted SMPTE and MTC coincides perfectly with where the ADAT tape is. So SMPTE time 00:30:30:00 is exactly 30 minutes, 30 secs on the ADAT tape. Cool eh?
Your method of transferring individual tracks would be this.
In you sequencer, mute all track that you DON'T want to transfer in it's internal mixer. Assign the track you do want to transfer to the Left or Right output of the sequencer, unless it is a stereo sound, in which case, you will want both Left and Output assigned.
Now, if it is a mono sound, and you say select the Left output for it, run the keyboards Left output into any track input on the ADAT. Record that track.
I should back up a sec here. You will need to slave your sequencer to sync with external SMPTE or MTC timecode. Also, you will need to possibly set a SMPTE Offset for the songs. Basically, what that means is that your sequencer usually, for SMPTE purposes starts at 00:00:00:00 time for each song. You don't want your ADAT's to always record tracks at that time. You get what I am saying?
So, your first song. You want it to start at 00:00:10:00, which is of course 10 seconds on the ADAT tape, you will need to set the SMPTE offset on your sequencer to start playing the first song you want transfered at 00:00:10:00, which means that when the ADAT reaches 10 seconds on it's tape, the sequencer will start playing from 0 seconds. Don't record any stuff to ADAT tape that starts before 10 secs. Also, you will want to start playing the ADAT at least 5 secs before the point that you want it to record. This is called Pre-Roll, and it is important to have at least 5 secs of it when you are syncing devices together. (In the old days, they would have to sometimes have 25 seconds of pre-roll to make everything sync right...how times have changed....

)
So, tranfer your first track. Now, mute that track, and repeat the above for the next track you want to record to ADAT, of course arming a new track on the ADAT to record too, and having the in's and out's between the keyboard and the ADAT all correct. As long as you don't set the SMPTE offset any different, when you play the ADAT, at 10 seconds on the ADAT tape, the sequencer will start playing from 0 secs. Thus, these two tracks that you transferred will be in near perfect sync! I say "near perfect" because SMPTE is not totally perfect, but for this purpose, and all practical purposes of this purpose, it will be in sync enough to where you won't hear anything wrong.
The method of hooking up the Data Sync 2 is to run the Sync Out of your ADAT into the Sync In on the Data Sync, then run the SMPTE out of the Data Sync to the SMPTE in on your sequencer. Then of course, set your sequencer to slave to incoming SMPTE, and set any offsets.
You can also transfer two tracks at a time from your sequencer if they are both mono tracks. Just pan one all the way to the Left output, and pan the other all the way to the Right output, and connect the two outputs to whatever two ADAT tracks you want to record them to. Easy enough, and that means only 4 real time transfers and you are done with the song.
Another thing about offsets. For your next song you transfer, you may need to rese6t the offset. Let's say that your first song, which started at 10 seconds on the ADAT tape, is 3 mins. 20 secs. long. That means it ended at 3:30 on the ADAT tape. You will want obviously the next song to start after that, and you should also leave yourself about 30 seconds or more between songs just in case you have another intrument that may need to be added in that maybe plays longer then the sequencer track does.
So, lets say that your next song starts at 4:00 on the ADAT tape. You will have to set your Offset on the sequencer to 00:04:00:00, which is 4 mins. so that it starts playing when the ADAT reaches 4 mins on it's tape. Got that? The new song is going to start on the sequencer at 0 mins, but you don't want it to record at 0 mins on the ADAT tape because you already have another song there, so you need to offset to sequencer to start when it gets external time code that is different then the Song Start on the sequencer. You could of course just go in and change the song start and stop times for the songs on the sequencer, but Offsets are easier to do really. Also, again, make sure to have at least 5 secs of pre-roll on the ADAT so that you make sure that the tape is running up to speed before it starts recording.
Repeat all the above until you have all your tracks and songs recorded on the ADAT.
A little warning. Your keyboards line output may not be strong enough to drive the inputs of the ADAT enough. You may need to run the keyboard to a line mixer first so you can turn up the volume to get the hottest recording levels on the ADAT's. Your keyboard MAY have enough output to drive the inputs of the ADAT though, and if it does, don't mess around with a mixer inbetween.
Also. It is a good idea to send a track sheet along with the tape that includes track assignements for each song, and exactly where each song starts. Including the tempo of the song is helpful too. All the infomation above will help the next person working with the tape know what is going on, and with exact start times for each song and tempos too, they could actually sync another sequencer to the ADAT and add more sequenced stuff to it and it will all be in sync if everything is working well.
Good luck.
Ed