Yes there is a O2 Booster Board :
The final circuit uses the OPA140 op-amp (FET input, DC precision, low THD+N) looped around an LME49600 audio current buffer on each channel to replace the O2 Headphone Amp's original NJM4556A output chips. Many other op amps would also work, such as the OPA827 and OPA627 with varying effects - see the full op amp rolling write-up in the build instructions. The board includes several optional "upgrade" modifications for the O2 headphone amplifier including an "anti turnoff thump" resistor, mosfet "on" indicator LEDs, and a 1/4" jack. The board produces a 93% reduction in the O2 amp's DC output offset voltage to around 20uV from the O2's standard 3mV. Output current capability is increased from 120mA per channel to 200mA for "music power" (playing music rather than sine wave testing). The O2's power supply has limitations that would prevent continuous current draw above 200mA per channel.
There are (3) versions of the pluggable PC board....check it out at DIY audio....