In Sonar I can load a synth, open the browser and use the synth to audition midi files.  What other DAWs do this? It's a great way to audition midi files and synth patches. 

Reaper is very fast and versatile when it comes to midi preview ...
All you need to do is load up a synth on a track or even multiple tracks w different instruments if you are doing midi drum preview w other soft synth sounds ...
To audition the midi files using the sounds you have pre selected just hit the track that has the instrument you want to hear ...
 
In my pic bellow I have a guitar vst for play back and the midi file I already placed on the track..
That is why you can see the notation ...had I not slid the midi on the track none of that would show up ..
The tracks below in the media explorer would have played fine ....FWIW I think this is a cool thing
 
 

 
all the best ,
 
Kenny

That's right. Any others? 

an Oldie but goodie

 
Kenny

It's not a DAW.

Cubase Pro 9.5 will preview MIDI in its browser through synths, with a sub window in the Media browser that lets you pick the MIDI device/input to send the preview to and a few other controls even.   Cubase's media bay and Media browser side window are better than SONAR's.

Studio One

Don't most do that?

I know logic does it and will even conform to song key

kitekrazy1
It's not a DAW.

I hate to break it to you Sport , Project 5 V 2.5  is a DAW .....it happens to excel at previewing Midi VIA multiple synths  .
 
I can understand if it is not a DAW you are interested ....still it would help for you to get your facts straight ..
If P 5 in not a DAW then neither is Ableton Live , Bitwig or SONY Acid Pro 7
 
Kenny