I purchased this PKP model for several formations for the Ost West Express. It's a brand I didn't know about and from what I could read, they might have some issues during the manufacturing regarding lighting.
In any case, I got the model and only realized later on that the same store - modelcenter.pl - has the related decoder. But it was too late. Later on, as I was looking for a sound decoder for my MÁV Class V63, I found this vendor: digitools.hu. I bought two sound decoders, one for the PKP EU07 and one for the MÁV V63 from this store: vasutmodell.com.
As it turns out, the speaker is already installed. You can see the 2 black wires right above the decoder going underneath the main board. Under the black wires, it is written SP- and SP+.
I tried to change the DCC address with JMRI, but DigiTools does not have profiles in JMRI, even though it is a recognized manufacturer by the DCC standards - CV8 = 75. I tried to use a NMRA generic profile, but it didn't work.
I then tried to use the engine with the default address #3 and the engine did response to DCC commands. And the sound did work which confirmed that the speaker was indeed installed at the factory. That said, there must be a short somewhere because the DCC-EX would reboot and restart after a couple of seconds. Thankfully, everything is protected with DCC Concept modules.
More investigation required ...