I own both Ety 4S and the SR-71. Yes it does add bass, but so does my portable Pimeta. The bass becomes a bit more defined with a little more definition and punch. It sounds perfect to me. However, the amp is not going to transform your Etys into headphones that give you huge bass, or have the effect of a bass boost. Also, the SR-71 will show it stuff more with a better source. It sounds good from my computer sound card, but through my portable DAC, it sounds amazing!! If you want an injection of major bass, the supermono with bass boost might be the best choice for your setup.
dshea