I've actually paired the XBA40s with the C&C BH amp that has been receiving many praise here on Head-FI. Compared to the E11s, preference wise, I definitely would still go to the E11s. The C&C BH definitely brings out the clarity with the 40s, and ultimately makes the sound signature from a U shape, to more of a flat response. However, the main thing I didn't like about the BH was that it affected the soundstage of the 40s a bit. There was definitely an increased clarity and detail (especially microdetail) with the BH, also,the instrument seperation was more pronounced and audible. However, I would still deem the E11 + XBA40 the best. The zout of the BH, on outout1 is 2 ohms vs the E11s 0.5 ohm. With the 40s being an extremely picky IEM, there is a synergy with the E11 that makes the layering of the soundstage more seamless. The extra clarity given by the BH overall removes the smoothness of the sound, and makes it a bit analytical (which was the sound I was trying to move from when finding an upgrade to the HF5s and ER4Ps). Lastly, I believe the extra ohms of the zout on the BH skews the 40s soundstage a bit (similar to the effect I had pairing it with the Sansa Zip Clip with a zout of ~1.5). The best way I can describe it is with the E11, the 40s place you right in the middle of the stage, with a good 5-10 feet from the L and R guitars, and the center stage vocalist/drums. The BH reduces the distance from 5-10 feet, to almost directly next to you, while increasing the centerstage depth.
I will audition both for a week to see how it goes if anything changes.
Edited by canikickit1 - 3/17/13 at 5:48pm