B400 is more comfortable to wear, has less bass warmth (especially sub), more vocal presence emphasis (nice sense of euphonic colouration - especially with female vocalists), but is a little subdued int he treble area. Personally I EQ 6-8 kHz up slightly. The B400 doesn't quite have the bass impact of the Andros, but is smoother up top. The 3.5 kHz is a colouration rather than anything else, and helps harmonics.
Both are warmish but balanced IEMs. Andro is warmish because of the relative bass to mids (higher). B400 is because of the relative bass to lower treble (bass is higher).
Different flavours - both good earphones (though I prefer Andro because of the lower treble emphasis - it suits my preferences more). Here's the measurement on my rig (click for larger):
Other options:
Andro and ES3 are somewhat similar - but ES3 is a lot leaner and Andro is tonally richer.
Here's the B400 and the Alclair Curve. The Curve is quite close to the Andro - but needs more bass and lower mid-range (easy fix with EQ or bass boost).
B400 vs the FH5. B400 has better transition through the mid-range. FH5 has more sub-bass impact, better build and fit, but is quite "shouty" in the vocal presence area (I need to EQ it down).