Do I even need a dedicated stereo preamp?

Your comment doesn’t allow for a quality relay attenuator built  into the DAC nor low impedance connections to a standalone pot, though.Can you pls elaborate further on what a pre does under those premises?

@antigrunge2 Actually that is what I was trying to address.

A low impedance control might work in some cases, and others not so well. It depends on if the source can drive the impedance without increased distortion and loss of bass. So you can see in some cases that would work well and totally not in others. If an active line stage were used it would simply work.

WRT to the relay operated control, that suggests a higher end DAC where the idea of a digital volume control isn’t trusted. So then it comes down to how well the unit can control the interconnect cables. IME most of the time the answer to that is ’not so well’. 

A DAC set up this way that has a balanced output that supports AES48 (the balanced line standard) would likely work just fine. 

NEED? No.  I have a very similar setup to yours, Anthem MRX540 driving 3 active fronts (Hypex powered) and 2 surrounds.  Do I want a stereo preamp? Yes! Why? Color, and the use of an external DAC.

Let me break it down.  Color would come from a juicy preamp, especially a tube pre.  The external DAC component in this particular case comes because the Anthem MRX line, as far as I can tell, has no analog bypass.  Everything you put into it gets converted to digital first, then re-expressed via DACs after.  Another issue is the limited range of digital onputs.  It has no USB asynchronous input, no Roon support. 

I’ve resolved these issues via a Pi 5 / Roon via HDMI, which lets me get to 192k/32 bit audio, but it’s not asynchronous and my Mytek DAC has to sit unused.  If I had a separate 2 channel preamp with HT bypass I could hook up any DAC I wanted to directly to the preamp and the output would remain in the analog domain. 

My advice is to spend no money until you have personally evaluated any options.  

OK so I bought a Holo Audio Serene lol. It doesn't have HT bypass but XLR2 and setting the volume to 0 does the trick. Anyway. 

Definitely worth the purchase. Darker background, more depth to the soundstage, which is much more noticeable going back to the Anthem. Switching back makes the sound more 2 dimensional. Going back to the Serene makes it more 3 dimensional. 

One interesting thing I didn't realize until some users here pointed out, is that the Anthem re-digitizes the signal. I thought some songs I would listen to had inherent distortion in them. I was wrong. It must have been the additional conversion in my chain that caused the distortion. I no longer have those parts in those songs show any distortion. Music sounds cleaner and more refined. Again, this is most likely because I am avoiding the extra conversion. 

On another note, hearing the attenuator clicks is SUPER satisfying. 

Now I want to play around with HQPlayer to see what upsampled music is like for fun. Does anybody know how to stream music from Tidal into HQPlayer without having to use Roon?