Getting a CX23885 based DVB-S2 card to work..?

Hi there,

i am stuck troubleshooting an issue with a small server, based on older hardware which i recently setup for my father-in-law.
I had a Hauppauge Starburst2 (which is CX23885 based) laying around, and i though that one might be super to setup a tvheadend installation on an old Intel i3-2130 (z77 based board).

I am using dietpi 8.14.2 on na native PC (x86_64). I installed tvheadend from the snap store, but its unable to find tuners. I dont succeed in troubleshooting this, so thats why i am posting - hoping to get some help from you guys.
There is a (german) article in another forum which states that, what i am trying to archive is basically possible but requires some tuning.

https://forums-gentoo-org.translate.goog/viewtopic-t-1093112-start-0.html?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

This article is referencing to a support article from hauppauge which can be found here:
https://www-hauppauge-de.translate.goog/site/support/support_linux.html?n=FAQ.Linux&_x_tr_sch=http&_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp#tv_tuner

I completed the installation steps mentioned in that article.
But i am still unable to find tuners with tvheadend.

Here is the information i got so far:

dmesg says:

[ 7.796098] cx23885: cx23885_dvb_register() allocating 1 frontend(s)
[ 7.796100] cx23885: cx23885[0]: cx23885 based dvb card
[ 7.796459] cx23885: cx23885_dvb_register() dvb_register failed err = -22
[ 7.796461] cx23885: cx23885_dev_setup() Failed to register dvb adapters on VID_B
[ 7.796464] cx23885: cx23885_dvb_register() allocating 1 frontend(s)
[ 7.796465] cx23885: cx23885[0]: cx23885 based dvb card
[ 7.900832] cx23885: cx23885_dvb_register() dvb_register failed err = -22
[ 7.900837] cx23885: cx23885_dev_setup() Failed to register dvb on VID_C

I am able to see the device using lspci:

05:00.0 Multimedia video controller [0400]: Conexant Systems, Inc. CX23887/8 PCIe Broadcast Audio and Video Decoder with 3D Comb [14f1:8880] (rev 04)
Subsystem: Hauppauge computer works Inc. CX23887/8 PCIe Broadcast Audio and Video Decoder with 3D Comb [0070:f02a]
Flags: bus master, fast devsel, latency 0, IRQ 19
Memory at fe400000 (64-bit, non-prefetchable) [size=2M]
Capabilities: [40] Express Endpoint, MSI 00
Capabilities: [80] Power Management version 3
Capabilities: [90] Vital Product Data
Capabilities: [a0] MSI: Enable- Count=1/1 Maskable- 64bit+
Capabilities: [100] Advanced Error Reporting
Capabilities: [200] Virtual Channel
Kernel driver in use: cx23885
Kernel modules: cx23885

I got the following lines from my syslog:

Feb 13 18:58:43 zeitgeist kernel: [ 6.519102] cx23885: cx23885 driver version 0.0.4 loaded
Feb 13 18:58:43 zeitgeist kernel: [ 6.519199] cx23885: CORE cx23885[0]: subsystem: 0070:f02a, board: Hauppauge WinTV-HVR5525 [card=52,insmod option]
Feb 13 18:58:43 zeitgeist kernel: [ 6.873076] cx23885: cx23885[0]: warning: unknown hauppauge model #150300
Feb 13 18:58:43 zeitgeist kernel: [ 6.873076] cx23885: cx23885[0]: hauppauge eeprom: model=150300
Feb 13 18:58:43 zeitgeist kernel: [ 6.955489] cx25840 10-0044: cx23888 A/V decoder found @ 0x88 (cx23885[0])
Feb 13 18:58:43 zeitgeist kernel: [ 7.086152] cx25840 10-0044: firmware: direct-loading firmware v4l-cx23885-avcore-01.fw
Feb 13 18:58:43 zeitgeist kernel: [ 7.715282] cx25840 10-0044: loaded v4l-cx23885-avcore-01.fw firmware (16382 bytes)
Feb 13 18:58:43 zeitgeist kernel: [ 7.795939] cx23885: cx23885[0]: registered device video0 [v4l2]
Feb 13 18:58:43 zeitgeist kernel: [ 7.795995] cx23885: cx23885[0]: registered device vbi0
Feb 13 18:58:43 zeitgeist kernel: [ 7.796098] cx23885: cx23885_dvb_register() allocating 1 frontend(s)
Feb 13 18:58:43 zeitgeist kernel: [ 7.796100] cx23885: cx23885[0]: cx23885 based dvb card
Feb 13 18:58:43 zeitgeist kernel: [ 7.796464] cx23885: cx23885_dvb_register() allocating 1 frontend(s)
Feb 13 18:58:43 zeitgeist kernel: [ 7.796465] cx23885: cx23885[0]: cx23885 based dvb card
Feb 13 18:58:43 zeitgeist kernel: [ 7.900842] cx23885: cx23885_dev_checkrevision() Hardware revision = 0xd0
Feb 13 18:58:43 zeitgeist kernel: [ 7.900847] cx23885: cx23885[0]/0: found at 0000:05:00.0, rev: 4, irq: 19, latency: 0, mmio: 0xfe400000

As far as i get it, all the neccessary kernel modules are already loaded:

(from my config-5.10.0.21-amd64):

CONFIG_VIDEO_CX23885=m
CONFIG_MEDIA_ATTACH=y
(for example - as far as i can see all the required modules are loaded by default - because i never changed/touched this)

Any help / suggestions are appreciated…