Hell no it won't fit haha. On the UD3P AM3 motherboard (granted that it's a reduced ATX form), the Mugen2 covers the DIMM slots completely. What is your rig for? I never really see the need for high-end RAM on most consumer uses (gaming, etc.).
I use the computer for some gaming, some video editing, some graphics work but also use if for work so I have several VMs running on it.
Anyways, most of the 6GB kits out there run at least $165 (except for the OCZ ones which from what I've read are giving people lots of problems and don't run anywhere near what their specs say) so I figured an extra $15 for memory that seems to be universally liked, has lower latency and requires less voltage isn't too bad.
Like I said earlier though, if there's some other memory that isn't going to be a major headache that's less, send me a link!