I haven't heard the A5 or A5.5 but I guess they sound more or less the same as mine (A308) but with more power...
Needless to say the i30 is a great amp.
The main fact that made me decide for the MF A308 is that this amp doesn't give you anything special until the volume control is set to 45. Taking in account that the volume range is 0-79, this means that you have to set the volume up to more than the half of it. With the i30 you can make something crazy that you would no do with any other amp that is turning it to the max volume and you can stand it quite easily. If I just can no t stand mine at the half of its volume. But this is just anecdotic and doesn't say anything about sound quality.
The sound quality in the i30 is superb and offers lots of detail but I found it to have a too much laid-back sound. That's nothing bad if you like it. But, I found the MF hights sweeter and better defined and what makde the diffreence (and what made me decide) is the extra dose of power that shakes your body (even at low volumes) with every change in the music.
That's my opinion only and is based in my experience which is short and poor in the HIFI world.