Problem with outboard DACs is that you will not be able to decode SACD layer off of your Marantz spinner (unless you buy a Marantz DAC). What Marantz CD player do you have? Two options to consider to replace your Marantz CD player are 1) the Oppo BDP-105 which is a universal player plus has digital inputs (USB/Coax/Optical) so you can use its DAC with PC/Music server sources and other spinners if you like, and 2) thee Marantz SA-8004 CD/SACD player which also has a USB-accessible DAC to connect a PC or music server to. Both units will play your SACDs but of course they are disc spinners so redundant with your Marantz player. If playing SACD through an outboard DAC is not an issue (i.e., you want to use an outboard DAC to play CDs from your Marantz player plus hi-rez files from a PC or music server), there are many outboard DAC options that are excellent in the up to $1K range:
Budget DAC (<$500):
1) Meridian Explorer USB DAC ($295)
https://www.meridian-audio.com/en/collections/products/explorer-1000/4/
2) Micromega MyDac ($399)
MyDac
Mid-level DACs ($500-$1K):
3) Music Hall DAC 25.3 ($599)...did very well in a shoot out done by members on another audio site to be nameless

against McIntosh D100, AMD DP-777, McIntosh MDA-1000 and others, punching well above its weight. Has a tubed output stage.
.:: music hall audio :: dac25.3
4) Meridian Director ($699)
https://www.meridian-audio.com/en/collections/products/director/37/
5) Musical Fidelity M1DAC ($799)
Musical Fidelity | M1SDAC DAC
6) Rega DAC ($995)
Rega Research Limited
7) Used Wadia 121 DAC (under $1K)
121
8) Used Bryston BDA-1 (should be able to get one in the $1K range) or a used Bryston BDA-2 (probably closer to $1.3-$1.5K if you can stretch the budget) BDA-1:
Bryston Limited: BDA-1 External DAC or BDA-2:
Bryston Limited: BDA-2 External DAC
Hard to tell what will be an upgrade as not sure what your current spinner is but this is a pretty good list for you to consider. Again, if playing SACDs is important to you via the new DAC, your only option is to get a new spinner that plays SACDs and has an accessible DAC as well. otherwise you will need to get digital separates from Esoteric or dCS or EMM which have transports that can play SACDs and can strip out the DSD stream and output it to one of their outboard DACs but then you are talking tens of thousands.
Hope this gives you some options to research and read up on. Good luck.