[Indread]

The O2 amp has relatively low stereo crosstalk. Would placing this in front of an amp with high crosstalk reduce it?
 
Also, would double amping affect the Dolby Headphone surround effect negatively (for example, placing an O2 amp in front of a Mixamp as opposed to listening to the Mixamp's source directly)?

 

[Head Injury]

Double amping is additive. If an amp with high crosstalk is fed a signal, the signal it outputs is going to have high crosstalk. Another amp won't reduce that, it will at best take the signal it's given and add nothing else to it. A clean amp like the O2 only has one job, which is to pass on the signal it's given. It's not supposed to correct it. So if it's given something with high crosstalk, it'll give you high crosstalk.
 
Likewise, Dolby Headphone effects will remain. But so will any noise and distortion (and crosstalk) from the Mixamp. There's no point to it, unless you need more volume or whatever sort of connectors the O2 provides.

 

[stv014]

Using the O2 after a bad headphone output may improve the quality, possibly including the crosstalk (if it was high because of too high ground impedance on the output, like e.g. with the AMB Mini3), since the input of the O2 is a much easier load to drive than a headphone. But it still only makes sense if the low quality headphone output cannot be avoided.