Just to keep all the "DE-5000 IR interface" info in one thread, here is my successful setup.
I've used the PT908-7C side-looking phototransistor (not from Digikey, so no guarantees it's original - but works reliably in this use case).
Friction fit "chassis", CP2102-based USB-to-TTL UART with USB-C connector. 1kΩ resistor from RX to 3V3. It works with 10kΩ as well, and anything in between, but rising slope gets uncomfortably slow, so 1kΩ is better.
The logic low level (when PT is open) is about 800mV, a bit high per CP2102 specs, but there must be good margin there, because with different pull-up Rs I saw it at just above 1V - and CP2102 was still reliably decoding the pulses.
The logic high is around full 3V3 rail (about 3.45V).
It will work with pull-up to 5V rail as well, CP2102's max V on any IO pin is 5.8V if I recall correctly, but I took a safer route.
Drivers used are Silicon Labs' v. 11.3.0.176 (VCP drivers) - works well under Windows 11 Pro 23H2 with latest patches. To install these - download them from Silicon Labs, unpack, then go into Control Panel - Device Manager, find CP2102 there, "Update Driver", choose from local disk (point it to the folder to which you've unpacked the drivers).
The software is from IET Labs website, for DE-6000, works well, just choose which COM port the CP2102 lands on.
Don't forget to press the "Play" button in software and the "PC" button on the DE-5000 to see the results :-).
I'm attaching a strip of photos and the PT908-7C datasheet here for reference.
I hope this will help someone!