Still own/listen to single driver towers (transmission line) that I commissioned 16 years ago. The drivers are Fostex F200a (8 inch, AlNiCo, rated 30-20,000 Hz, 8 ohm, 90 dB/w/m, no stinking whizzer cone). But they're not perfect. First, got the drivers EnABL'd (treated to help midrange/treble extension/clarity). Then added "Late Ceiling Splash" tweeters ala Duke LeJeune to address the high frequency "beaming" and widened the sound stage. Finally added 3 carefully placed subwoofers ala Floyd Toole et. al. to address inherent in-room bass peaks/dips. They're not perfect but suit my room, tastes, and genres well.
I've owned better: JBL 708P (2-way active monitor, 8 inch ported woofer, 1 inch wave guide loaded tweeter). The 708P is the best loudspeaker I've ever heard. It was uncolored, coherent, and very dynamic/room filling. Obviously I have an affection for the active concept (single driver loudspeakers by default active). The wave guide, which on the 708P looks like a horn, provides controlled directivity and thus helps them sound the same regardless of the room, thus is a current favorite feature among designers.
You're smart to go for the "ideal" loudspeaker first, but doubt if anyone can DIY an ideal loudspeakers short of having the resources of decades of design experience, a team of researchers, at least $100k of testing equipment, and in-house manufacturing facilities (pulling drivers off the shelf like most manufacturers do is a compromise). Same with amplifiers and all passive loudspeakers. Very few companies can fit that bill (active design, wave guide, and deep R&D/manufacturing resources).
Secondly I'd suggest working on the room (shape, size, insulated, possible treatments). After ordering my commissioned loudspeakers I had a dedicated yet practical listening room built: 8ft x 13ft x 21ft; insulated staggered stud walls; exterior insulated fiberglass door with weather strips; flexible lined/insulated ductwork; 6 GIK 244 full range absorption panels at first reflection points; 4 GIK 244 bass traps straddling the front corners; and 3 tall randomly filled bookcases to diffuse sound along side walls. Your large room is probably ill shaped, it could be cut down.