Upgrade to PS Audio Direcstream Mk1 and Mac Mini?

I’d have to think adding a good pre like the Lamm would bring significant improvements, but definitely something well worth a try.  You could do a trial of the new Spatial Audio Raven preamp that’s getting fantastic reviews.  I’d keep the streamer and DAC separate as you’ll have greater flexibility to pick a DAC with the sound characteristics you’re looking for.  

The first thing I would do it get the mac and all macs, out of your system.

Best options are - 1) keep your Roon Core away from your system; 2) if possible don’t mix streaming and DAC (network cards in DACs are typically not the best streamers)

The preamp section of the PS Audio DSD is not horrible. But in my experience a good dedicated preamp will be an improvement over the preamp section in the DAC - more natural sound, better soundstage and better tone.

You can get a really cheap computer to run your Roon Core on. Then as @soix suggested pick up a Lumin U2 Mini or the older model U1 Mini. Either one is going to be an improvement over the mac mini.

One other thing - in my experience there are pros and cons with using Roon

Pros: Roon has the best UI and convenience factor. Another advantage of Roon is the Roon radio feature that continues selecting and playing tracks that match the playlist or last song you played - I’ve discovered a ton of new music that way.
Cons: Roon sounds softer, rolled off and not as musically engaging as most streamers proprietary UI/processing. i.e. Auralic sounds better when its Lightning DS software is used, Aurender sounds better when its Conductor app and processing is used. There are different paths taken to reproduce streamed music. Lumin is one streamer that sounds more or less identical with or without Roon and has a very user unfriendly Lumin UI so using Roon with it makes more sense.

There are dedicated streamers that are also designed to be used as Roon Core and supposedly they are a no compromise units…think Grimm MU1 and MU2, top of the line Innuos. But they’re in a different price category than the PS Audio DAC.
Something to think about. Oh and the Grimm units have a built in DAC.

So if your budget is limited to say $5,000 - $6,000 I’d go for the best possible streamer and be ready to potentially drop Roon and use Qobuz and or Tidal.

…think Grimm MU1 and MU2, top of the line Innuos. But they’re in a different price category than the PS Audio DAC.
Something to think about. Oh and the Grimm units have a built in DAC.

Just for clarification, the Grimm MU1 is Roon Core (Server) and Roon endpoint (Streamer)  The Grimm MU2 is all this PLUS DAC.

I have the Grimm MU1 with a Tambaqui DAC and it sounds excellent, and yes a different price point.  And, while I agree to keep streamer and DAC separate, the MU2 seems to be a combo unit with little compromise.

@fastfreight thank you - I stand corrected.