*** Are you thinking of modifying more Oppo 105s for your friends? :b
Actually I do modify (now any of the Oppo models issued so far), for anybody who may need it, want, or ask me to do it. More or less friends... I do not discriminate any of them...
There are some main improvements for these devices, which it may be common to all models: replacing the original SMPS with a linear PSU to power the digital board. Improving the clock system, which as original is a very simple and standard approach. Improving the analogue output stage of the device. For 105 models is is also the power system for DAC chip (which is critical for the quality outputted by this advanced DAC inside), as the analogue power system for the analogue stage of the player.
If you may think to some improvements for your 103 device, we can also go into details (PM). I may suggest as principled business rule in this field: buy a used 105 player and then send me the boards to fix it. A little bit technical skils may be necessary from the user side, to dismount and mount again the boards, and connect some connectors (of course all necessary instructions included). Done!