We have a steam shower and the generator is in my closet in the master bedroom, it is on the other side of the shower wall. We have a thermasol, it's over 20 years old and still works perfectly.

We have a Kohler steam generator in our basement, about 12' horizontally from the steam head in the shower. Its a good idea to periodically flush the steam generator as minerals can build up in them (the steam is pure water, the minerals remain behind.) The drain fitting on ours is plumbed with a ball valve to our sump pump so the steam generator can be periodically flushed. If it were in the attic, my guess is that the generator would rarely get flushed, if ever. I would opt for a nearby closet. There is a bit of rumbling on start-up as the supply line fills with steam but during operation it produces a constant low-level whoosh sound. Insulation on the lines helps the noise as well as reduces heat loss, the steam temp being 212F is above the temp rating of the box store pipe insulation. Pre-shaped high-temp fiberglass pipe insulation can be purchased from sources on-line.

you have an unfortunate location , you really want to avoid tight spaces and attics, if ever a repair needs be done you want it accessible. I will go to great lengths to make sure weve got a drip pan and an overflow (in this case you cant see it but weve run the overflow to the hose bib for the laundry units as its on the 3rd floor. And boy am I glad as i had to repair this unit. I would likely use the closet and place the unit up high as to be sure all water runs out of the unit and out steam head after every use... Really the location would be chosen based on electrical panel and hopefully an overflow drain option, distance and repairability. I always suggest upgrading to an ADK auto drain kit or auto flush depending on brand generator you use