I have heard neither ! However I have a MF A3.2 and my previous amp was the MF A3. The MF brand delivers excellent quality from my experience with the two amps I've owned. Both amps you refer to are an upgrade from mine, I'd just go for the one with the most appealing spec for your requirement. If you like the MF house sound, you're unlikely to be disappointed with either.
I seem to recall the A1008 was the next model from the A5. The A5.5 was/is an evolution of the A5, so the A1008 should be better than the A5.5. If you get the chance to listen, go for the better sounding one, and if you cant split them, go for the cheaper option.