If your pi 1 has the correct headers, you can use the:
WOLFSON AUDIO CARD - AUDIO CARD, FOR USE WITH RASPBERRY PI. (google and find f.i. element 14 )

Its successor for the 40 pin GPIO header is sold-out and no longer produced. But the original version for the pi 1 is still available, and was recommended many times for its audio quality.
The original drivers are rubbish, the support from the manufacturer is even less, but we did manage to get good working raspberry drivers from "HIAS", and put support in PCP.
see: https://forums.slimdevices.com/showt...rt-in-PCP-3-20

Yesterday I tested the PCP6.0.0 B7 on my production set ( B+ and CLAC ) and the menu's allowed me to get the card setup in 5 minutes.
So there is little risk these cards do not work for you.

If I only had a compatible pi 1 .....

Regards M-H