[MENTION=5078]fpj1[/MENTION], so you want to have strong wireless signals all around your house + Media server / File server. Well its easy.
I'll call nayatel modem (a) 1st-floor (b) and basement (c)
1) If basement and 1st floor modem got wireless options
If both modems got a wireless option just bridge them with your nayatel wireless modem. Turn off the DHCP option on both modems (b and c). Give it a manual in this sequence
(a) Main gateway/router = 192.168.1.1 (just follow the series you are already using but in this pattern)
(b) = 192.168.1.2
(c) = 192.168.1.3
You can assign modems IP from accessing it from their default IP via browser then change "Router IP"
Once you do it, simple bridge it with (a) by going to bridging option, giving IP of the main Modem (a), its mac and wireless channel. Thats it. Also, on the main modem (a) keep the DHCP on and exclude the addresses you assign manually to (b) and (c).
2) If (b) and (c) don't have wireless option
Just connect it using ethernet wires (networking cable in simple words) but connect in the simple ports (not the WAN ports). Actually both ports will help you share the internet but WAN port creates different IP segments. Like if you connect (b) and (c) via WAN ports it might be something like this
(a) 192.168.1.1
(b) 192.168.2.1
(c) 192.168.3.1
The only issue that people face in such method is file-sharing. It needs some extra configuration.
Also, turn off DHCP on both (b) and (c) and assign it manually as stated in the previous option. Install the PLEX Media Server on your System and it will be accessible all around the house
Hope that helps.