no, there is no additional io,
the adc/dac within Axoloti only supports for 2 channel in and 2 channels out.
(the headphone output is not separated from the main output)
so you could do this if you used a mono on the return, and a mono main output.
to go beyond this, would require you to add an additional external adc/dac, and then coding support for this into the firmware.
in the future its hope there will be the possibility of connecting multiple Axoloti boards via a digital link which would include multiple audio channels.
this would allow for the possibility of using another Axoloti for the analog IO, e.g. for external effects such as filters. albeit, this would introduce a little latency.
note: there is no release date planned for this yet
axo 1 -> (digital) -> axo 2 -> (dac) -> filter
<- (digital) -> axo 2 <- (adc) <- filter
-> (dac) main output