Audiophile newbie in need of DAC/DAP.

Hi, this is my first posting as a new member.

I am a long time devoted piano student and after spending a good amount on a really nice electric piano, my kids chipped in and got me Fostex TH900 (used) headphones for my 50th Birthday.  My fiance read a review somewhere and scored a used Fostex HP A8C amp. 

None of us are audiophile savvy.

After doing some research, it seems a waste not investing in a similar level player to fully enjoy this "partial" setup as I currently only using them to hear myself practice on my keyboard.

Despite several reviews I've read saying these are primarily "never leave the home" use rather than your typical portable headphones, I am looking to invest in a portable DAC/DAP.

Any recommendations would be greatly appreciated! 

Thanks
H