If you do not need phones out and unballanced connection would do.... You may use output of phones, you just need cable that splits TRS to, say, two TR (or cinch).

Or you may add another DA to digital outputs of UCX II, like Ramses has suggested. If money is concern, there is also ADI-2 (still avaible new for about 400 EUR) or newer ADI-2 FS. But for sure those Pro are really cool.

I think he refers to analog / balanced outputs, as you can see on the product photo, there are 6 in the back of the unit.

Well in many countries, even in EU, the price of interfaces like ADI-2 Pro and like may be more than monthly income. For example average income in Czech Rep. is less than 2000 EUR before taxes and obligatory health, social care and pension payments. So, average person might get about 1400 EUR netto monthly.

It is way far from one lunch. There are not just US, Germany, .... folks using RME.

Ramses did. And what DA would you suggest to OP? DA that is on par with those in UCX II. Even ADI-2 (not ADI-2 FS) at current sale costs about 400 EUR, but it is big exception because of final clearing old stock at local distributor...

Interesting and thankyou (everyone).  The purpose for the additional outs is to run a surround system for DIY acoustic panels run via exciters/transducers.  There will be as many as 7 panels and a sub woofer, so 8 outputs.  The panels run on standard speaker wire.

I use the UCXII for standard music production applications but need it to be capable of running these panels in a surround system.  But I am uncertain what would be the optimal device (to pair with the UCXII) which would interface with the speaker wire coming from the speakers/panels/transducers.

What kind of amplifier and where to hook it up to the UCX that would allow full control inside TotalMix?

I haven't read anywhere that there is an upper limit for the budget.
And with his setup, I still think it would be an excellent way to expand the monitoring section.

Even if someone sets an upper limit, I have often experienced that it was a limit against better judgement and the limit was not so fixed after all, but the better solution was chosen.

It was also the first product that came to my mind because of the many useful functions for monitoring.

An application can only load one audio driver at a time.

So … if you use two recording interfaces, you need devices which use the same driver so that the application can access the devices through this one driver. You also need to take care, that the devices use the same buffer size and that the devices are clock synchronized.

If you have Apple, it might be a little bit different due to the possibility to create aggregate devices. But also here I guess it would be an advantage to have the same devices to have the same type of converter and thus same converter latencies.

A disadvantage with such setups is, that there is no backplane between those devices, you have to route through the DAW if you want to route audio from one to another recording interface.

If I read that you want to implement a surround system, then it might be easiest / best to use devices with the same converters to have the same converter latency. You should have mentioned your use case upfront.

If you need 8 output channels, then UFX II would have been best as it offers 8x D/A using the same converters and it supports RoomEQ if you need it. This is also independent of sample rates as those analog ports are directly attached to the recording interface.