DAC Or Server - What to upgrade first?

I'm wondering what will give me the biggest upgrade in sound, a new music server (Aurender N10 or W20) or a new DAC (PS Aaudio Direct, Simaudio 780D, Berkeley Refence DAC, etc). I currently use a Meridian Sooloos MS600/MD600 server/storage system and a Berkeley Alpha DAC 2. Any experiences on where the best place to invest in an upgrade would be?

Rest of the system is Simaudio P8/W8 amplification and Revel Studio 2 speakers.
Several of the better known audiophile server companies such as Aurender and Antipodes now offer less expensive versions of their top-sounding servers that play files from a NAS as well as provide for streaming music. It might be a good time to try one and get your server/source nailed down. Your Berkeley Alpha DAC 2 is recent and well-regarded and observing how much better your system sounds after upgrading your digital source might help you figure out where you eventually want to go with your DAC. Just my 2 cents.