Do you have this one ? https://www.mil-media.com/HV-3D-8.html
It directly supports Dante, AES or MADI digital output modules.
So .. what recording interface do you have ?

We should find out what makes more sense
- to upgrade the device itself with a A/D converter or
- to get a separate A/D controller

A solution could also be a new RME recording interface supporting MADI like the UFX+
which is currently very affordable and to equip the Millenia with a MADI module.

But there are also other RME MADI interfaces available.

I only want to mention that this might be the best solution for you, more scalable, etc.

For guitaristic reasons I have an Antelope Synergy 4 thunderbolt that have 4 headphones out and some interesting modeling effects, useful for having comfortable listening while tracking. While I'n not totally in love as interface this features are very handy for my needs

OK, the Antelope only has 1x ADAT i/o.

Cabling / Signal flow would be:
Millenia Preamp -> Analog out -> 8-port A/D converter -> ADAT -> Antelope

You could use for this purpose:
- https://www.rme-audio.de/de_adi-8-qs.html (with MADI)
- https://www.rme-audio.de/de_adi-8-ds-mk-iii.html (without MADI)

Alternative Proposal. The analog section of the UFX+ is already superb.

Get an UFX+ which you can get currently to a very affordable price.
Its an USB3/Thunderbolt recording interface.
By this you get a solid base, TotalMix, MADI, Durec, Everything you dream off.
TotalMix FX has now TotalMix Remote and so on.

Then I would connect
- Millenia analog to the UFX+
- Antelope as Guitar Processor standalone to the UFX+ via ADAT

Voila, best scalebale solution with zillions of good options and advantages.

Later you can still decide, whether you give the Millenia a MADI module and then you can connect it per MADI.
This frees again your analog ports on the UFX+
AND ... you are even abale to record up to 192 kHz by this, because
- you connect the millenia now directly to the UFX+ analog ports
- and later you connect it via MADI, at 192 kHz there are still 16 MADI channels left

This would be a much scalable high quality solution.

Then buy an ARC USB on top, then you have very comfortably working.

1 year later (if you have cache again) you can even add reference grade quality D/A conversion for phones and monitors by integrating the ADI-2 Pro FS to the UFX+, for monitors and phones by ADAT or AES.

See here: https://www.tonstudio-forum.de/blog/ind … our-Setup/

I think this will be the best solution for you.

If you want to keep Antelope for guitar because of its effects, then you need to find out,
whether its capable to run in standalone mode.

Alternatively keep it connected via USB just to control the inserts / effects of the antelope or to load the routing for this setup which should be quite easy.

Otherwise you benefit from a high quality RME based setup which even allows you to scale in the future,
as MADI allows connection of even more gear.

You are flexible, because you can connect the UFX+ via thunderbolt, USB3
and even USB2 but then the MADI channels are inactive.

DURec, Autoset, FX effects, TM Remote, Digicheck, ... Really LOTS of features and Scalability / expandability up to the integration of the ADI-2 Pro FS if you want that later in the future, which is also very very nice.