Routine installation. No big deal at all. It's the ONLY way that wood floors are installed slab on grade, which is 95% of all of the new construction around here. 7 1/2" W flooring will need really good humidity control in the home though if you want to minimize it's normal shrinking and swelling. Even engineered that wide will move a bit.

Please check with the manufacturer's installation instructions. Often in condos you have to install a wood floor over cork to deaden the transfer of sound. That is a wide plank, and unless the manufacturer recommends glue down, the plank may "cup" from the moisture in the glue.

Check with manufacturer because some floors must be installed unnailed and unglued with a space around the room for expansion. If there is no room for expansion the planks may cup from not enough room to expand.

Thanks for the replies. Update:

We had the wrong info from the sales guy at the flooring store.

Contractor says the layer of soundproofing he's buying from them CAN be nailed through without affecting the benefits of the layer.

So we're now going to nail down, 7.5" 5/8' thick engineered white oak on top of soundproofing layer (see link below, and if anyone's used this please advise if you're happy with it) on top of old plywood.

This is a condo built in 1979, overlooking the water in a Northeast climate.

Here is a link that might be useful: Sound Solutions acoustic underlayment

Hi Duchamp, I'm curious how your project went with nailing down 7.5" engineered oak? What soundproofing layer did you end up using?

From what I've read wide planks should always be glued, but curious to your experience?