Hi,
this you might already know, but good rule of thumb is to set the
levels manually for each source (according to its dynamics), having
peaks around -6dB to -10dB. If you have manual volume/gain control on
your recording device/preamp, I'd set all levels in the computer to
80% of the scale and then control everything by hand, on the box.
This probably doesn't apply to OpenBSD, but in Linux there have been
serious distortion trouble with levels set to 100% on some older cards
- the only solution is AFAIK try it out and use what your ears tell
you.
The good news is you can do other stuff while your LP's spinning and
recording :-)
-- 
Martin Pelikan