> I have two main questions before I buy - firstly would it be better to get the Fireface 802 running on the firewire
> card already in my PC? Or would there be benefits to replacing the firewire card with a thunderbolt card and
> getting the Fireface UFX 11 or UFX+?

You will have more benefits when getting an UFX+.
Some details about the device in my blogspace: https://www.tonstudio-forum.de/blog/ind … 8-RME-UFX/

And how you can expand with MADI: https://www.tonstudio-forum.de/blog/ind … Cber-MADI/

I wouldn't base something on Firewire anymore. You mentioned Win10. The legacy firewire driver is still available as separate download, but at a certain point it could happen, that changes in the Windows kernel take place and the driver won't be updated anymore...

> I realise that in the 802 and UFX 11, I can connect 2 x ADAT but as I need to add more, can I also use the
> Digiface USB at the same time? Will my PC recognise both units and address them correctly and reliably?

Digiface USB and UFX+ use both the MADIface ASIO driver. Then the DAW will use the one ASIO driver and see/access both devices. You only need to consider
1. you need to clock sync both devices by connecting both with a digital link (so you have to sacrifice 1 ADAT I/O for synchronizing both devices)
2. you need to take care that both devices always use the same ASIO buffersize
3. you need to work with two TotalMix FX instances / windows and you can't route audio between those two TM FX instances. Inside of the two TM FX sessions you can route inside TM FX as you want. Routing between the two interfaces would only be possible on DAW level.
4. if you want to connect the UFX+ by thunderbolt then this is not possible anymore. The Thunderbolt driver is a different driver than the MADIface USB driver. Then the DAW can only access one device at a time.

> I am thinking that I might have to go to the UFX+ and then use a MADI converter to handle all of the
> inputs and outputs but this looks like it might get very expensive!

This would be one solution to get an ADI-648 if you want to stay with the current conver
https://archiv.rme-audio.de/products/adi_648.php

Or alternatively you sell them and fully convert to MADI, this saves you the additional costs of an adi_648 (€2444).

And alternative solution to the UFX+ would be to think about an HDSPe MADI FX PCIe card with 3 MADI busses.
I reviewed such a card here: https://www.tonstudio-forum.de/blog/ind … ro-FS-BE/, check out the separate PDF file.
This is the only PCIe card with the full implementation of FX chip and has 3 MADI busses.
With an optional card you can switch the 3rd bus from coax to optical as well.
It has an analog out for phones and a very nice AES I/O port which makes it ideal to connect an ADI-2 Pro FS R BE for monitoring purposes and the connection of phones with all the nice features of the ADI-2 Pro FS R BE.
Another cool feature is the special ASIO driver for the HDSPe MADI FX that only allocates resources for audio channels in your PC, if those channels are active. If I remember right this goes in blocks of 8 channels, I described this in the PDF that you find inside of the Blog article for download.

Otherwise the UFX+ with DURec is a very round solution if the
- 64 MADI channels  @44.1/48
- 32 MADI channels @88.2/96
are enough for you depending on sample rate and the final amount of devices.
A very nice feature set in 1 RU.

This is how I use the UFX+ and DURec: https://www.tonstudio-forum.de/blog/ind … -DURec-DE/