Magnepan IIa AMP recommendations

I just bought these, and I must admit I am not a ribbon expert at all. They say 6 ohms on them. I hooked them up to an Onkyo TX-890 (125 WPC IIRC) and they sounded 'dull'.

What do I need to drive these properly ?

Would a Mac MC2105 do it ?

Do they need a specifically marked/made 6ohm output (as the 2105 has) ?

How about an Onyko M-504 (150WPC) ?

One of them had the fuse out when I tested them b4 buying, but it seemed to work (a little I guess with my 35WPC receiver)...why is that ?