High performance, low power consumption options?

[audiomuze]

Looking at CPU specs these days it seems pretty hard to discern one from another in power consumption, performance & chipset terms, so I'm hoping for some advice as to CPU and motherboard options I can consider for an upgrade...details below.

Basic requirements:
- high performance when under load, very little power consumption when idling
- (5 or more) 2TB low power hard drives attached
- drives will be spun down when Idle for 5 mins or more, PC ideally into sleep mode
- will run headless
- Activity on NIC must awaken PC from sleep mode
- PC's only purpose is to run Squeezeboxserver & MusicIP and to serve video, photos and documents to HTPC/AV/HDTV
- Music collection is in the region of 12-15k albums
- will be connected to gigabit LAN via CAT6
- no RAID or other storage schemes - just straight SATA connections with each drive being an independent unit.

Any ideas as to suitable CPU & mobo combinations appreciated - would prefer to build my own pc rather than buy something that's pre-built.