Advice needed on rt5645 config, debugging

Dear list-members. New to the list and an archive search didn't help so 
far.
I'm trying to use the internal sound of a lenovo miix 310 tablet (intel 
atom x5-Z8350 based). It's an alsa-only configuration. Sound works with 
an external usb soundcard when blacklisting the kernel modules for the 
internal sound device.
It seems that I'm having a rt5645 device. But I cannot play anything on 
it. With the many channels and options this device has, the ucm rules as 
well, I'm stuck. My basic question is: How can I figure out where the 
problem actually is? Is the hardware not supported? Is it a routing 
issue? Any other things I need to check?

Some of the things I tried with output:
aplay -l:
**** List of PLAYBACK Hardware Devices ****
card 0: chtrt5645 [chtrt5645], device 0: Audio (*) []
   Subdevices: 1/1
   Subdevice #0: subdevice #0
card 0: chtrt5645 [chtrt5645], device 1: Deep-Buffer Audio (*) []
   Subdevices: 1/1
   Subdevice #0: subdevice #0

alsaucm list _verbs:
   0: HiFi
     Default
(for alsaucm, I've created symlinks in /usr/share/alsa/ucm/ for 
LENOVO-80SG-MIIX310_10ICR-Cavalli, pointing to chtrt5645, then: alsaucm 
open chtrt5645)

cat /proc/asound/devices
   2: [ 0- 0]: digital audio playback
   3: [ 0- 0]: digital audio capture
   4: [ 0- 1]: digital audio playback
   5: [ 0]   : control
  33:        : timer

cat /proc/asound/cards
  0 [chtrt5645      ]: chtrt5645 - chtrt5645
                       LENOVO-80SG-MIIX310_10ICR-Cavalli

I also blacklisted the hdmi module in /etc/modprobe.d/blacklisted.conf:
blacklist snd_hdmi_lpe_audio

aplay someSound.wav:
ALSA lib pcm_direct.c:1824:(_snd_pcm_direct_get_slave_ipc_offset) 
Invalid value for card
aplay: main:828: audio open error: No such file or directory