I dunno bout the dlink dsl604t being good with low snr, but its a crap router, I've had 2 of them and both of them died the exact same way, they start to hum and loose connection to the pc but still stay connected to the adsl line, avoid that one if you can.
you know when they start to go, as you end up with more and more disconnections which only last maybe 10 seconds tops, then it gets to a point where you cant even access the web interface for the router...
apart from that, in their first 6 months, they are good, but just seem to have a short lifespan, well thats what I found out, especially if you get one of the versions that have a high pitched hum to them.