Music Server/Player for NOS R2R DAC

I'll spare the long story but have recently decided to adopt a new DAC that is a NOS based design and is limited to S/PDIF for input. Once I have it and have had time I'll post my observations and impressions for sound quality. Suffice it to say I am taking a different path from the direction many are going. My music collection is redbook CD converted to FLAC. I am currently using an Atoll MS-100 streamer/player. Very simple interface, software is simple but effective, and initially I will continue using this player.

I am in the process of selling my Esoteric K-07 CD player and have no plans to spin discs going forward. I am not seeking ROON, etc type of interfaces. Prefer keeping FLAC files on either a USB drive or internal hard drive.

So all that said.. told you I would spare the long story!!!... I am curious what music players/servers are out there built very well, great power supplies, and something that would be  a step up from my Atoll. HAS to have RCA S/PDIF output and preferably its own software.

I have identified  a few players thus far but many do not have a coax output.I am quite ok with buying used or demo and would like to keep my price under $5K (preferably less). PLayers I have found thus far which would work are:

Aurender N10
Lumin U1
Auralic Aries G2
DCS Network Bridge

I could buy a higher quality USB to S/PDIF converter but would rather avoid that.

I'll see how this goes ones the new DAC arrives and I experience NOS and R2R for the first time. Am very hopeful it will bring to my ears that which I am seeking! But, looking forward I am wondering what would be a good upgrade from my Atoll. Thx