Yup- I'll bet you a beer that it is a patching problem. It also might possibly be a clock probem, but only if you are either using an external clock source, external converters, or both. If you just got the box I doubt that that's the case- so let's focus on the patching thing.
The D160 as delivered has only 8 A/Ds. So to record on track 9, you connect your input to the D160's input 1, and enable track 9. Sounds like you have that part done. Only question is, what is on the *input* to channel 1? If you've left it patched up from monitoring the drum mix, you may well be simply feeding the output of track 1's playback right back into the #1 input. This is especially likely if you are driving the Fostex inputs with channel direct outs from channels 1-8 on your board.
Think about it: if the outputs from tracks 1-16 on the D-160 are put into line inputs 1-16 at your board (a likely setup), then the direct out on channel 1 will have the playback from tape track 1 on it *by default*, unless you explicitly repatch something somewhere. It gets worse: on some boards, like
my Alesis Studio 32, there is no mic/line switch. So whatever is on the line input, and whatever is on the mic input, get *mixed together*. Meaning, of course, that the mic signal loses, since it is probably 40dB or so lower than the line signal. This can certainly drive you _nuts_ until you discover it.
It can be moderately painful to work out a working style with this going on. Even with an inline board like the Studio32 (which has entirely separate tape return/monitor inputs), the mic/line commoning problem is a downright pain in the ass. I want a freakin' switch there!
Anyway: repatch the D160's inputs to the direct outs on the appropriate channel, don't just reuse channel one on the mixer to try and track with *in addition to monitoring* (unless you have an inline-monitor board, which is probably not the case). If you are using direct outs, move the Fostex input 1 to the direct out of (for example) channel 9, and just use channel 1 to monitor what's on track 1, and use channel 9 for your overdub.
The bottom line is that you need to separate your monitoring function (the channels used for existing tracks) and the recording function (the new material intended for unused tracks) to separate channels on the mixer, and that absolutely requires repatching. I personally let the recorder track assignment drive my channel assignment on the board: board channel 9 is _always_ associated with Fostex track 9. Thus, I'm constantly changing the patch for the Fostex input #1 between direct out of channel 1 and 9 at the board. That is, until
my AC2496 converter box showes up, giving me 1 A/D per channel and simplifying that part of my life to no end.
Hopefully, that makes some sense... If not, post more details about your rig. However, the only way that the D-series machines will duplicate one track onto another is by external analog feedback, or by using the internal "track dupe" function. Whatever is happening here is external to the box.
