Cheap/simple relay/resistors attenuator for RPI

And as a mid 2020 update for anyone considering buying one of these for use with Volumio. Volumio advertise it on their site, and say that it can be used with GPIO spacers, as mbrennwa describes "up thread". Not these days it can't. And indeed I don't think it will work stacked on Allo Piano or similar either with current Volumio.
Allo & Volumio have not updated the plugin needed to make this work since late 2017. Meanwhile Volumio have been busy updating their core product.
The plugin software uses 2 sets of lower level code called wiringpi and LIRC.
Current Volumio uses kernel 4.19, and this means that the LIRC software will definitely no longer work. Wiringpi may work but is unsupported these days.
Posted questions on the Volumio page for the ARA are ignored.
If anyone is successfully using one of these on current Volumio 2.779, I'd love to know more about how you're doing it.

Cheers

Paul E