The CA-9100 can either lower or add gain.
I've been told it starts adding gain when the knob is at eleven o'clock.
The knob cannot be locked at different levels (+5dB, +10dB, +15dB...).
To be honnest, I totally occulted that post from 2 years ago.
I've been taping with the 4061 and a battery box since then.
Never tried the preamp.