Comment by nicoburns
kyube or kyoob would definitely be the way to go.
It's funny you use "tube" as an example though, as in my British accent I pronounce that as "chube", whereas I believe many Americans would use a "t" sound for that word. Not sure how you settle on a spelling in those cases.
Regional variations are available! I think the BBC would have had it pronounced tyoob. And don't Americans pronounce it "subway"?