This makes absolutely no sense.

1- 1st of all .. you have now the AIO, its paid (€619) and its an excellent card for your purpose.
Do you want to sell now, loose money and buy the Digiface USB new (€359) ?
From selling you will most likely get the €359 for the Digiface, but ...
it makes absolutely no sense, you will loose money by this and get finally an interface which doesn't offer features and
quality of the AIO.

2- If you use VSTis in your DAW then this can stress the CPU much, depending on the CPU hunger of the VSTi's
and your project size. In such a case people prefer PCIe bus based solutions, as USB has more protocol overhead
compared to a PCIe bus based card and uses eventually tad a bit more CPU time to transport data.

3- the analog section of the AIO is much better. The handbook has all of this data, SNR, THD, ... simply take a look yourself.

I propose that you keep the AIO its much better for your purpose and even has such nice things like ADAT, SPDIF, AES, MIDI, additional dac for phones and can be expanded by various expansion boards.

The Digiface USB has its "right to exist", no doubt about it, its a fine interface for its price and its main focus (mobility, easy to handle, 4x optical SPDIF if you need, etc ...). But if you have already a phantastic PCIe card like the AIO .. simply keep it.
You have already excellent RME gear for your purpose.