The media shouldn't make a difference whether cable or fibre. For Dual Access PPPOE (AKA Russia PPOE) your first connection is to the providers resources and then a PPTP connection is setup to the Internet as discussed [here] [0] Since you have a router that does this in firmware, I would continue to use that as it allows for more flexibility in your LAN and is the simplest solution.
Dual access means a two-staged connection with the Internet service provider (uplink):
connection to the provider through Ethernet-interface to assign an IP-address,routes, etc. with DHCP or with static settings.
•connection with the use of the protocol group like “point-to-point”, (PPPoE, PPTP,L2TP) on the second stage
Connection to the provider network is carried out through Ethernet-port ; an IP-address,routes, name servers are assigned to the client by the provider.
Upon completion of the first stage of connection a client gets access to the internal resources of the provider, but not to the Internet.
On the second stage the connection through PPTP or L2TP protocols is established with the assignment of a new default route, new name servers and a new IP-address on the new interface ( named pppX). Upon completion of the second stage a client obtains access to the Internet.
this should give you some idea of what your router is doing for you behind the scenes. Your ISP should be able to provide you with all the information required to connect. In effect you need a PPTP connection setup over your initial connection to your ISP. If your initial connection isn't stable enough for you to have time to setup the PPTP connection over it, I would discuss the problem with the ISP.
As an aside, many cable internet providers use a registered MAC address to determine network access. (This is how it works in my neck of the woods) You can likely locate the routers MAC address on the Status page under WAN as shown in Figure 4-1 Router Status on or about page 17 of your router manual. Then you can change your Ethernet cards Mac address as decribed here.