I gave up on the software/firmware route for this topic on both my HTC 8X and also my Nexus 7 and just went with a little Fiio Fujiyama-E06 amplifier. Cost about ?20 iirc (not at cheap as an app, but works for any hardware).
Works a treat, and it's tiny (about 4cmx4cm), and runs for 6-8 hours on a full charge (recharges via mini-USB). Lives in my kit and cable bag that tends to nestle in my pocket. Usually use it for watching movies on one of the two devices when flying easyJet around Europe - it has enough grunt to make soundtracks audible above the aircraft noise.