Thanks for all the replies! Feel a bit silly now...
I have ordered the 2nd CPU with a passive heatsink and the VRM and will fit them as soon as they arrive.
The reason I went for the X346 was I bought it on Ebay for an amazing price! The other server I have is a dual Opteron based machine which I built myself around a Tyan motherboard and 3ware SATA RAID card as I needed huge disk storage...so I do prefer Opterons usually!
Thanks again for everyones' useful comments.