FreeNas server upgrades

[Scott17818]

so I have an old Dell XPS 410 running FreeNAS with a

intel dual core 1.86ghtz,

4 gigs ram (yes I know below the threshold of what FreeNas is happy with)

2-2GB WD greens (yes I know greens, but they do ok-ish, with ZFS)

 

currently running latest distro of FreeNAS

I mainly use my server for storage, and Plex media server

 

my current issues:

not enough ram, or CPU power to decode and re-encode most of my HD movies. 

 

the good:

case can support another 5 HDD's but I assume with most dell cases I'd have to re-drill for proper ATX/mATX boards

 

what I'm looking at is the possibility of an ATOM powered MOBO quad core preferrably, and 16-32 GB of ram. to be able to do ZFS caching. is this possible with the Dell hardware/case? any drawbacks to running a low power ATOM processor for video encoding on the fly? I like the fact of a lower power bill, but not at the expense of poor performance over what I have now. and how cheap can I go?

 

I have 2 dell 410 cases to nab parts from, as well as an older Sony Vaio case with all it's parts. both are similar CPU's. intel pentium D1.66ghtz, and bothe the 410's are 1.86ghtz dual cores. Just not sure if I would be able to use the stock PSU, and how difficult the cases would be.