On mine, MBM reads the internal diode 8 C less than MBM reads it. If your BIOS is reading 56 C you're probably ok IF you are reading the interanl diode...BUT.
I dunno what mobo you have but it sounds like your are reading the socket right under the chip (since MBM and the BIOS are reading the same temp). In that case 56 C is pushing it a bit because your cpu core is probably around 66 C
You could always fix a panaflo somewhere near the HS for good measure or just live with it running a tad on the high end.
Mac