The Infrant ReadyNAS NV+ / 2 Squeezeboxes Bundle ($1500) is a heck of a deal, especially if you have an external DAC to use with the Squeezebox. I have basically the same setup (although I bought my ReadyNAS from NewEgg rather than Slim Devices), and am very happy with it. Using a RAID 5 configuration with the ReadyNAS will give you something like 700KB of storage with safety if a HD goes bad, enough for about 2000 CDs using FLAC lossless compression storage. The sound should be more or less the same as your Accuphase if you use it as the DAC for the Squeezebox. Setup and operation is pretty straightforward, and with the ReadyNAS you don't need to have a computer on to listen to your library (you do need it for setup and for storing CDs).
You could always go with the higher end Transporter plus a ReadyNAS, which should be right around $3K. But the performance differences between the Squeezebox and the Transporter are supposed to pretty much all be in the DAC and analog sections, so the upgrade would probably be a waste if you're going to use your existing DAC.