I grabbed an Infrant (now NetGear) ReadyNAS NV+ recently to replace my Linux server, and it is supposed to support both the 360 and PS3 out of the box. I've tested the PS3 (DLNA certified client), I'll try and see how it works with the 360 sometime soon and let you know.

I'm not sure what adding Twonky would do, but the Readynas is on the list of supported devices there, and it's the only device listed as "Easy to install TwonkyMedia add-on authorized by the device manufacture"

I'll try to type up more later, but I chose the Readynas for several reasons, with the key ones being performance, expandability, and support. Their community is amazing, with high developer interaction, even during the post buyout timeframe with Netgear.