What's my ideal music server? Read and recommend please

Have you looked into what the capabilities of the M1's MDx processor module upgrade are?

https://bricasti.com/en/consumer/mdx.php

Looking into the owner's manuals, you can use the Bricasti as a network DAC for a UPnP/DLNA server. 

My guess is that if you discussed this with the folks at Bricasti, I would not be surprised if they consider this the best sound quality option for the M1 DAC, and you can then explore a good NAS option. If you wanted to get "audiophile", the Innuos products would probably work best.

The Innuous products are functionally an integrated NAS without a bunch of storage options on board. There are many Linn and Naim users who host their UPnP server on an Innuos or other products like it (Melco). I would not be surprised to find other Bricasti owners to be using the MDx with an Innous or other NAS using UPnP/DLNA and getting exceptional results.

On this note, this is also to me a huge blind spot on the part of Aurender. There is absolutely no technical reason Aurender could not include a feature to install a DLNA/UPnP media server on any generation of music server they have produced. It's a Linux machine running Ubuntu after all. Why not give a customer the flexibility to use the product in a different way if they decide to move/upgrade from a USB-based DAC to a network-based DAC? It's plainly obvious by now to anyone paying attention that network based delivery, whether it's UPnP/DLNA, Ravenna, Dante, Roon, or whatever comes down the pike, is how DAC manufacturers (including Bricasti) are improving their products and bringing them to the future. An Aurender customer owning an M1 DAC wishing to experience the MDx upgrade will be left sitting on a brick which can't deliver files over a network connection in any meaningful way. Sure, the Aurender software is nice, but there are plenty of easy to use media software apps. Their attitude is actually quite tone deaf, as is shown by their introduction of products which are essentially an Aurender-only, glorified NAS drive with CD ripping (the ACS10 and ACS100). Cornering these products to solely the Aurender ecosystem is a foolish approach, when they have plenty of capability to run a Roon Core or UPnP/DLNA server and give clients much more flexibility.

The MDX board is superb. It’s been fitted in my M1 since July 

I wonder if this is doable and a viable solution- continue to use my MacBook Pro and use a Bricasti M5 renderer between my laptop and the dac 

So just how pricey are these Bricasti products? (M5 in particular) There literally isn’t a dealer within 1,000 miles of me and their website doesn’t even show an MSRP on any of their products. As a career marketing manager, I have a very negative initial impression of any company who does much of their business exclusively on the net, but intentionally does not post an MSRP.

I have a bricasti dealer a reasonable distance from my home. List price is easy enough to find on the internet any by and large companies that don’t direct market don’t show prices on the internet. One of the advantages of living just a bit north of NYC- just about anything is available within an hour or 2 drive at most. Heck, I can get to McIntosh Labs in 3 hrs. 

Zavato
Just get rid of your mac book pro.  When I went from my MacBook to the Sonore Signature Rendu SE the improvement was HUGE.  This unit acts as the renderer or client.  It also handles the streaming.  My Small Green Computer is where my music collection of 7TB lives.  It has an one board drive for ripping CD's.   It is similar to a Roon Nuc but has better components and was made to my specifications with a 10 TB Solid state hard drive.  The server and the renderer run proprietary "Sonic Orbiter" software which integrates the two units flawlessly.      For playing music the combo runs Roon which is the best platform.   My experience with setting up this system was truly plug and play.  Support from SGC and Sonore has been very good.  
This digital front end cost about $8K.  I run it thru a PS Audio direct stream DAC.  This fairly "humble" front end  is able to make my Nagra HD electronics and Wilson XLF speakers truly sing.
I can state the following with certainty:
1.  The best server is the Taiko Audio, bar none.  ($30,000)
2.  Aurender W20SE is probably 2nd in sound quality, but doesn't do ROON  and I LOVE ROON.  A friend loves his N10.
3. Innuous Statement, Antipodes EX/CX combo, Wolf Audio's higher end are all  excellent choices.
4.  In the end I chose the SGC Server as Andrew was willing to put in 10TB SSD for a reasonable price as I have a large music library,  and  the Sonore Signature Rendu SE because of excellent reviews.  (I spoke with one of the reviewers and he purchased the Sonore)
5.  Any of these options will be an obvious improvement in SQ, reliability and ease of use over the MacBook, especially if you get ROON

BTW you have a great DAC.  Almost bought one, but just purchased a Rossini instead.