I have the same setup that I did because my D5 Next virtual flow sensor was so inaccurate that it kept tripping the Alarm even though my flow rate was around 225l/hr. I also noticed that when I set the flow sensor type to #53068 the flow rate numbers reported by the D5 Next were pretty far off from what my High Flow Next reports. I found that setting the flow sensor type to #53291 (high flow LT) resulted in numbers that were much closer to what the High Flow Next reports. I asked about this in the Aquacomputer Support subreddit (under r/Watercooling). Here is a copy/paste of the conversation.

I purchased cable #53294 from your online shop and did the following:

I connected the cable, set the HFN Signal output to generate the high flow #53068 signal, and set the D5N Flow sensor type to the same #53068. It worked, sort of. The D5N now reports 241l/hr while the HFN is reporting 224.4l/hr. It is much closer than the D5N virtual flow sensor, which is what I was hoping for.

Now my question. Out of curiosity, I also tried setting the D5N flow sensor to each of the other options in the pull-down menu. All of them gave me incorrect values except Aqua Computer high flow LT #53291. When I select this, the D5N flow rate goes from 241.1l/hr to 227.0l/hr which is much closer to what the HFN is reporting (224.4l/hr). It seems to be MORE accurate than when I set it to high flow #53068, even though that is what the Signal output of the HFN is emulating. Does this make sense? Is it OK to leave the D5N flow sensor set to high flow LT #53291 even though the HFN Signal output is emulating a high flow #53068? Why does setting the D5N flow rate to high flow LT #53291 give me a MORE accurate reading than when I set it to high flow #53068? I would prefer to leave it this way since it causes the D5N flow rate to be practically identical to what the HFN is reporting.

Shoggy (Aquacomputer rep) responded, Our programmer changed the calibration values in the software a while ago but these changes have not been adapted for the firmware of affected devices. So, some combinations like yours do not match at the moment. That will be adjusted in the future.

This was 5 months ago. AFAIK, they still have not updated the calibration values. I don't know if they forgot about this or if they are waiting until they have to update the D5 Next firmware for some other reason. He mentioned further down in the discussion that the chip that stores firmware for the D5 Next has limited capacity and they are already having trouble getting new firmware to fit.

Here is a LINK to the discussion. You have to scroll down a bit to get to the part about the calibration values being off. BTW - Aquacomputer tends to respond to questions more quickly on the Aquacomputer Support subreddit than they do on this forum.