Onyx 1200f: headphone outs as "regular" analog outs for recording when using standalone?

Folks:
 
I have a couple older interfaces that I no longer use as interfaces but as multi-channel preamps, such as the Mackie 1200f and the Presonuse Firestudio Tube.  I use a Lynx Aurora for conversion.
 
Problem is that they have fewer apparent analog outs than ins.  So, the 1200f, for example, has 12 decent mic preamps, but only the d-sub 25 for analog outs (8 channels).  There are, however, four headphone outputs.  Can those be used simply as additional analog outputs, or is there something functionally different between a "normal" analog out and a headpone out?  I could route the extra four inputs to the four headphone outs and run those to the Aurora to record all 12 channels, converting via the Aurora.  But should I?
 
Same question for the Presonus, though it only has one headphone out - usable?  If anyone has these interfaces or otherwise knows how to maximize analog outs to match analog ins, I'd really appreciate your help!
 
Thanks!