I think you will have to apply the reasoning;- ?don?t raise the bridge, lower the river?.
Could you rearrange the deck chairs & present a avenue / thrust staging. Rather than flat on seating & thereby reduce the depth of the rows, by placing them into a horse shoe on 3 sides of the acting area. [in the round]
I feel you will have more problems with bar stool or with taller chairs, with the punters who are shorter at one end, than you could wave a stick at!
You could always grade your audience by dressing the house military fashion, ?tallest at the back & shortest at the front?. Even rigging up a electronic  light beam [LDR] height sensor alarm,  at the house entrance &/or low tech hanging clearance bar across the aisle to the front rows. But it would need to be monitored by ushers "You can?t bend your knees sir to get under" or "Excuse me madam, you will need to take the wig off to sit closer!"
If it is just a step height, it would be easy enough to knock together a step rostra, as you suggest or even just rake the back for a couple of rows. Obviously raking the stage is out of the question, unless you only use height impaired actors &/or rearrange the blocking with dressage for the warm props being the directing criteria.
Back in reality I guess it would be around a 6? - 7? ceiling Or are you just exceptionally tall?
I doubt any of this would help!
What type of ceiling is in the basement, is it a floating under cement type or just lined?