Is it possible to find an Amp that has an audio optical in port in the rear of the box, with a 6.3mm headphone port in the front?
This must be the most common arrangement between the DAC/amp combos. There's no shortage of options, but to get any practical advice you should be more specific: budget, headphones to be used with, is it for music only or also movies/gaming etc.
not to nitpick but no amp in the world has an optical input. Amps can only have analong inputs where as DAC can have a optical input and most DAC/AMP combo's will have optical. Check out audio-gd nfb-10 or 5 or etc etc or fiio e17 or ....there are several hundred options...