You can adjust the output level of each channel individualy. The level adjustment applies to both the RCA outputs and the headphone jack.
You cannot change the stereo bus mix channel panning. Channels 1 & 3 are always hard-panned left, channels 2 & 4 are always hard-panned right. If you want any other panning (except a mono, see below) you will need an outboard mixer.
You can output to the RCA jacks as either individual discrete channel outputs (unmixed) or as a left/right hard-panned 2 channel mix. In addition, you can use the headphone jack as a seperate independant output, and select from a mono mix of all 4 channels or the same hard-panned stereo mix as is sent to the RCA outputs (other 'non-mixed' headphone output monitor options are: mono solo output of any individual channel, stereo pair solo of either inputs 1/2 or 3/4, and mute).
The limitation is the panning, not the channel output levels.