Check out Earthboxes and City Pickers/Patio Pickers. They're made by the same company in Pennsylvania and they do combine hydro and soil. I've got eight of the Patio Pickers in two 4x4 tents going right now and the girls love it. You assemble the thing then pack soil in the corners then the rest of the soil goes over a screen covering a reservoir underneath. You add water through a tube that sticks out from one corner of the box. You can't overwater because excess will run out a pair of vents on either end. Water wicks through the soil and a mulch cover or actual mulch on top of the soil keeps moisture in. The plants eventually set down water roots into the reservoir where they have access to all the water they need plus a oxygen in the air gap between the top of the water and the soil screen. Once they set water roots, you can tell the difference in how the plants' growth takes off. I grow in living soil, worms and all, in my pickers. Except for pests, I have no issues. I don't adjust pH (and shouldn't anyway with living soil) and simply add amendments to the surface every three weeks. Plant trimmings can be used as mulch and you can go no-till and simply keep growing new batches in the same soil until you're practically growing in a worm bin.
Back to the main part of your question - Gnats aren't a problem if you use mulch or the mulch covers that come with the pickers. Neem meal as a soil amendment also discourages them. I did have my troubles with hemp russet mites, but that went back to last fall before I starting using living soil. I think they came in with some backyard compost I was experimenting with in coco. I didn't catch the real issue for months and blamed environment, nutrients, etc. and new generations of plants just kept getting infested from the older ones they were mixing with. I'm hoping to score some predator mites when the grow shops around here start stocking them. Check out Clackamas Coot's soil recipe if you want to mix your own so you know no pests are present. Some grow shops have ready-made living soil. I bought several bags of Build-A-Soil 3.0 when I bought the pickers and added it to my homemade soil because I had nowhere near enough.