how did you end up with /dev/sr0? sounds like thats the dvd media that came with the nas. srX is normally scsi/sata optical devices. based on the error from the mount command the volume is not being mounted at all? can we get a `showmount -e 192.168.1.122` is it at all possible to ssh into this...
if you connect to the ddwrt router (if able). what ip/netmask/gateway do you end up with?
i haven't done this in a while but i don't think 'router' mode is needed since your ddwrt will just bridge your current network and not be routing a new net
your ddwrt is not running dhcpd correct?
6120 and 6121 can bond up to 4 channels download and 4 upload
6180 can bond up to 8 ch down and 4 up
the 6121 is newer than the 6120
6180 is the best for 'future proof' but youll have a hard time finding a place to buy it, your local cox store will either sell the SB6180 or a cisco...