Does Apple TV1 work without HDMI connected?

I use my Apple TV (first generation) as an audio player, feeding the optical out to a DA converter and using the Remote app on my iPhone to control playback.

The Apple TV used to be connected via HDMI to my flatscreen too, but I rarely used it (the screen was often in stand-by mode and this worked fine)

I have moved my TV to a different room, so the only difference in the configuration is that the Apple TV1 is no longer connected to a screen using HDMI.

Now, when I select a track on the Remote app to be played, it looks like a moment it's gonna play (on the iPhone screen in the Remote app) but then quickly jumps back. Everything else works as expected - the Apple TV shows up in iTunes, I can sync it, and I can select the Apple TV as a speaker output in iTunes and get audio from it. So the only thing that does not work is play audio content that's stored on the Apple TV internal drive.

As a test, I connected the Apple TV to my flatscreen again (using HDMI) and then audio playback worked fine again.

So, it looks like it needs to be connected to a HDMI screen in other to work properly, even if I only want to use it as a standalone audio player.

Is this true? Or is there something I can try to have my Apple TV work standalone again, without a HDMI connection?

Thx for any help on this!

Ivo