MPC-HC also has a "volume booster" option as well that goes up to 300%.
Note however that it's not a magic silver bullet - the louder the source material is, the worse the quality will sound for a given boost amount.
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____HTPC____ | __Desktop PC__
2.93GHz Xeon x3470 (4c/8t Nehalem) | 4.5GHz 1.24v dual-core Haswell G3258
Radeon HD5870 | Intel iGPU
2x2GB+2x1GB DDR3-1333 | 4x4GB DDR3-1600
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