The headphone amp board doesn't have anything on the back panel other than a mounting screw.   It also has a small cable going to the main input buss board.   It does have a top panel jack for the headphone TRS 1/4" standard plug for your stereo headphones.      

Pictures on how to open up the o2r for service are in this listing.  Each of these boards are held in a cage and screwed into the back panel.   Take off the cage cover and slide the base of the board off the pin connector and pop in this replacement board.    

Here is a demo video of the o2r which also has a close up of the display.  https://www.youtube.com/watch?v=5nWi-Pe46as  

Item must be returned within 30 Days and Refund of purchase price shipping not included only will be given as: Money Back via pay pal or through the method paid. Buyer to pay return shipping as well. 3% restocking charge if item not broken. I don't end auctions early. Buy-it-now items are in my ebay store. If you have a concern about your purchase please contact me, as I work hard for your satisfaction starting with prompt shipping.

International Buyers Please Note:

Import duties, taxes, and charges are not included in the item price or shipping cost. These charges are the buyer's responsibility. Please check with your country's customs office to determine what these additional costs will be prior to bidding or buying.