Streaming Transport without DAC- few choices

I already have a very good DAC. I already have a very good preamp. There seems to be a dearth of streaming transports under $2000 which noes not include a DAC, does not include preamp function or does not include both. 
So tempted to just get a Mac mini and use that as a dedicated transport/server, played through audirvana 

iFi just released their new ZEN Stream which looks nicely done for $399 .. WiFi & ethernet connections, USB & SPDIF out, and sans DAC to name a few features.
If you're interested in Roon, they have a Nucleus which hosts their software and acts as a streamer for $1500.
At one point in time I had a mac mini with audirvana feeding a Berkeley alpha usb which was feeding a Berkeley alpha dac. Out of boredom I purchased a Raspberry PI and installed Roppieexl to try streaming. I then compared the direct Mac connection with the Mac streaming to the Raspberry pi connected to the Berkely. I found minimal sound differences between the two setups.

you mean a streamer, or a transport?

you said 'transport' in your title, that means something that will spin a cd and read the bits on it...
I’m very satisfied with the sound of the $800 Pro-ject Stream Box Ultra S2. It’s based on a Raspberry Pi with the power supplies and analog sections optimized for low noise. It certainly sounds better than a laptop or iPhone that I used for a short while. At some time if I get bored with time on my hands, I’ll compare it to more expensive streamer/transports to see if anything else sounds better. I'm thinking Innuos or Auralic. I’ve heard the Naim NDX 2 used to play back local files from a flash drive through my Pontus II DAC. It sounded good, but wasn’t noticeably better (at least without comparing head-to-head with my Pro-ject streamer).

You can plug a hard drive, solid state drive or flash drive into the Pro-ject streamer so it becomes a transport for local files.

The Innuos Zen Mini is supposed to be quite good as well.

In theory, a dedicated streamer will have less EMI and RFI than a Mac Mini or other general purpose computing device. Maybe buy a streamer used and see how it works for your needs?