No playback with Ardour and StudioLive AR16
I'm trying to set up a recording environment for my band with Ubuntu 16.04.3 LTS (kernel version 4.4.0-101-generic), Ardour4 and Jack 1.9.11. As an external soundcard I'm using a Presonus StudioLive AR16. Everything seems to work fine except for the playback. I've read a lot of wiki pages and forum posts, but nothing seems to help. The strangest thing is that it worked a couple of days ago and I haven't changed anything significant (?) since. Here's what I do:
I start Jack via QjackCtl. Before I start Jack, I choose my StudioLive AR16 as interface in the QjackCtl settings. As server path I use /usr/bin/pasuspender -- jackd in order to suspend PulseAudio while Jack is running.
Ardour recognizes the Presonus interface, I can record and when I hit the play button, the master levels are moving. I checked the audio connections settings in Ardour: the master output is connected to the two system's playback channels. I controlled all the connections in the QjackCtl connections window - everything seems to be connected correctly, yet I can't hear anything. The interface doesn't seem to be receiving any signal at all. (The "USB return" button was pressed.)
I checked the playback levels of the interface with alsamixer, all 3 channels are on maximum volume.
I also tried reloading alsa - it didn't make any difference.
I tried aplay /usr/share/sounds/alsa/Front_Center.wav - the sound came out of the internal speakers of my laptop. Maybe for some reason Ardour tries to use my internal soundcard for playback? So I tried alsa_out -d hw:2 -q 0 after starting Jack it said the device was busy, so I guess StudioLive AR16 was set correctly as output device. But I still can't hear anything at all.
Has anybody got a clue how to fix this?