There is only one way to pronounce Hi-Fi. Because Wi-Fi is a play on that, there is only one way to pronounce it. That would be the first syllable of these two words:
Wireless
Fidelity
And don't go around calling it Wireless Fidelity either. That's no more descriptive.
Now, OP, show me one single CE ad with someone pronouncing it any way but the Hi-Fi-derived way if you don't want us to think you're an idiot.
Now, back in the '90s, I called a router both root-er and rou-ter (50%/50%) because the base word and verb (what it does), route, can be pronounced either way and they weren't mainstream enough for there to be things like TV commercials to draw from. All of my tech knowledge came from print and a primarily textual dial-up Internet. By the time I encountered IT professionals and learned that it was nearly universally called "rou-ter" in the US, I immediately adopted the accepted way to pronounce it. If you've been saying it wrong, you should too.
I happen to know that Ichinisan jokingly calls it "whiffy" from time to time.