I built a home theatre utilising two projectors to create a massive 3.5+ meter screen! Read all about it here. Also part of this home theatre is a home-built subwoofer capable of a flat response down to 35Hz, and I have a plan to get that down to 25Hz or less, using a home-built subwoofer amplifier and a Linkwitz Transform Subwoofer Equaliser.
Other plans include bi-amping the main speakers using a pair of 80watt Gainclones which I've already built (using my own PCB design, etched at home). Unfortunately I went bonkers with the torroid transformer, bought a hefty 700VA job that provides *just* a bit too much voltage for the poor TDA7293 chips I'm using, although they'll survive if I don't use high volume. Part of that plan was to use a pair of parallel chips bridged together (that is 4 chips each capable of delivering 80 to 100 watts), for a grand total of around 600 continuous, crazy, RMS watts! That's when I realised my subwoofer can only handle 350 watts peak! So what am I gonna do with the 10 TDA7293's I bought? :-P
I really get a kick out of using simple electronics to get massively improved performance out of consumer electronics. For example, with my above plans, I should be able to make my R5000 sound system sound like a R20000+ sound system. As another example, I want to build myself a CMoy headphone amplifier complete with cross-feed and the Linkwitz transform equaliser for the best headphone sound possible. This would probably sound better than any off-the-shelf headphone amplifier (even using cheap headphones), simply because I can tune it for the best sound *for my ears*.