On the Audio driver screen (from which you extracted the details you give above), press the Advanced button and check that your Realtek card is correctly selected there.
@Iain-Wright Shutting down and booting up is not the same as a clean reboot, just in case you never did that.
What audio devices are listed in the Magix Low Latency settings when you click on the "Advanced..." Button?
You can also try a different version. Just download the newest version from https://www.asio4all.org/ and install it. You can then select it as an ASIO driver in the program settings. Maybe your Realtek device will work better with the newer version.
As suggested I downloaded the latest ASIO driver and the hissing has gone. Thanks very much for responding so swiftly and sorting the problem. It is much appreciated.
If you are using Music Maker 2021 - you need to double the audio buffer sizes to avoid potential clicking on playback.
The results form @emmrecs comment regarding the audio devices/ports listed, may indicate that this is a driver issue.
I had an issue with Realtek HDA when Windows replaced the manufacturers driver with a cut down version, resulting in the loss of several in/out ports. Re-installing the genuine Realtek driver fixed the issues.
The ASIO4All has worked because it is a work around which bypasses the direct ASIO issue with the sound card.