Easiest way: configure D-Link with boot CD. No splinters before D-Link Modem necessary if no analog phone is used. (Via web interface IP 192.168.1.1, these settings are rather cumbersome).
Then select the options:
Country: Other
ISP: other
Protocol: PPPoA (particularly important because PPPoE is not only Gigaspeed use)
Encapsulation: VC Mux (Mux multiplexer is, VC-Based)
VPI.VCI: 8:48
VC / VP 8/48
Is there an annex A- POTS modem.