The closest coordinates given for the city of R'yleh in Call of Cthulhu are SL 49 51', WL 128 34'. The ship that landed at Cthulhu's resting place was at said coordinates a day before. Upon recording their location, they continued voyaging in their original direction, which was a route from (I assume) Norway, terminating in Australia.

That's the best I can say. That article doesnt really specify where the Deep Souns Channel is, so that's the most information I know to offer.

And, for the record, we all know it's Cthulhu.