Set recording level (WAV) on iRiver H140?

[Muse]

I'm going to do an interview at a music venue in a couple of weeks. I have an iRiver H140 and an iRiver H120 (with 30GB HD), and have been advised to use both recorders, one for me and one for the interviewee. I'm going to use the built in microphones on the recorders. I'm told by my helper that the quality of the result "will be MUCH better" if I use two recorders instead of one.  My helper has advanced knowledge of digital recording software and techniques. I will be meeting with him over the weekend and will bring the iRiver recorders and we will do some experimenting. He told me that I should be careful not to have my recording levels too high when I do the interview.

I looked in the menus in Rockbox and don't see anything where I can set the recording levels on the recorders. How is this done? I usually use one of these recorders to make MP3 recordings from line-in, and I seem to remember setting levels somehow, but I don't recall how. This, however, is to WAV and I'm going to use the internal microphones, which my experience tells me are pretty decent. Thanks for your help.