unfortunately not. You have the wrong version. there was 2 original white OpenReach modems, 1 ECI and 1 Huawei. They both looked almost identical. The Huawei can easily be unlocked with a simply firmware upload, and provides excellent stats. The ECI requires opening up, soldering, connecting cables, flashing, etc. After all that the ECI stats aren't as good as the Huawei.
The Asus is quite easy to setup as a router only. This is done under WAN settings > Dual WAN > select Dual WAN NO. Change from DSL to WAN and choose the Ethernet port you want to use as a WAN port. Options might be named slightly different I'm quoting that from memory, but you'll find it from that. Unfortunately you automatically lose 1 of the 4 Ethernet ports by turning 1 into a WAN port. Then to retrieve stats you need to use another port.
We're unsure how the Asus really performs, and how much DLM doesn't like it, as it doesn't provide the necessary ES/SES stats, and the INP values are incorrect. I know on my line, which is shorter than yours, the Asus would struggle to hold a steady 6dB SNR margin. My advice would be to seriously look into getting a new modem to run with the Asus, or to sell the Asus and get a new modem/router combo. Unlike when you bought your Asus, there's now a decent range of modem/router combos