PPPOE configuration

Hi, I would appreciate some advise/assistance in setting up my network.
Our ISP has allocated us a block of 8 static IP addresses - 6 usable
xxx.xxx.xxx.xx0 - xxx.xxx.xxx.xxx7
The network is connected to our ISP via an ADSL modem which is configured in bridge mode
I have a Mikrotik Routerboard 750 which has 5 interfaces
Interface 1 - connected to ADSL meodem
Interface 2 - network a 192.168.100.0/24
Interface 3 - network b 192.168.200.0/24
Interface 4 - network c 192.168.300.0/24
Interface 5 - network d 192.168.400.0/24

I want or connect each of the first 4 dedicated IP addresses to the networks
xxx.xxx.xxx.xx1 ↔ 192.168.100.0/24
xxx.xxx.xxx.xx2 ↔ 192.168.200.0/24
xxx.xxx.xxx.xx3 ↔ 192.168.300.0/24
xxx.xxx.xxx.xx4 ↔ 192.168.400.0/24

I have started out just doing the first connection
I added a PPPOE client with user name and password which connects to the ISP
I added a masquerade for 192.168.100.0/24 to IP>Firewall>NAT.

This actually works and it turns out that PPPOE client is allocated xxx.xxx.xxx.xx1 when it is connected. But I cannot find a way of specifying which dedicated IP the PPPOE connects to

If I could specify which dedicated IP address was used, I was planning on adding 3 more PPPOE clients (total 4), one for each IP address and specifying the each interface in the masquerade declaration

I would expect to have access at all the static IP addresses once the PPPOE connection is made.

I would like advice if this is the best way to achieve the result?
Is there a way to access all the external dedicated IP with one PPPOE client?
Is there a way to specify which external dedicated IP address the PPPOE client connects to
Thanks in advance

PS I There is only one gateway to the group = xxx.xxx.xxx.xx1 so everything has to go out through the gateway. I am not sure how to direct the incoming data on the dedicated IP addresses to the appropriate network
Thanks