What kind of freestanding lamps can I use for > 6000 lumen up-light?
You'd need sunglasses, if not welding goggles, to be in a room with 500W of LED lighting.

I like the Torchiere ("floor lamp") solution the best. There are dozens of available styles, colors, and prices.  The ones in my living room have translucent plastic shades and reading lamps (also with translucent shades), handle two 150w bulbs each (plus a 60W bulb for the reading lamp). It's plenty bright with three of these fixtures with 10w (!) dimmable LED lamps installed, and you'd have to be about 6' 5" to see over the top of the shades.

Similar lamp at Amazon

I find that Translucent shades give better coverage and eliminate more shadows than opaque shades (where all the light is coming from the ceiling).