FYI: The previous photo of some unknown persons "pile o' horns" appears to be:
Upper midrange: 1" TAD TD-2002 mounted to 650Hz Edgarhorn
Supertweeter: Fostex T90A or T925A.
Lower midrange: 1.4" PM phenolic RCA MI-95XX series (i.e., 9548, 9584, 9448) with "salt shaker" phase plug, mounted to older version of Bruce's 300Hz tractrix.
Midbass horn: Edgar 100Hz.
Regarding the stated uniqueness of GOTO SG-570 among drivers for covering 300-2000Hz, the Altec 1.4" 290-series, JBL 2" 248X series, JBL 3" 2490 and RCA 1.4" MI-95XX series were all designed to cover this range. All of them use phenolic diaphragms, accept 2490 using 4" titanium dome, 3" throat and low 5:1 compression ratio.
GOTO Unit product description says SG-570 has Beryllium dome and frequency response of 100-6000Hz, but is designed for 200-1000Hz. The GOTO is probably the superior driver, but considering the $12,350/pr MSRP of the GOTO and the fact that its not exactly easy to audition these in the states, I I'll be sticking with these high value American alternatives.
By "plugless", are you saying you reverse mounted the S2 on your horn?
It will be very interesting to watch and understand as you attempt to integrate the knees of all your drivers.