not my fave scenario but had to do it on my Edgarhorn 100 system to match midhorn - the 1/4 size 100Hz m=0.5 horn uses a JBL 2220H so above ~125Hz, sensitiviy is about 109dB 1W/1M - midhorn probababy 103 ss - JBL LE5 on 250Hz rectangular tractrix - bottom augmented by 1-1/8 size 40hz Monolith

in this situation impedance fluctuation is pretty benign so I got nice results running everyting including 'sub' with homemade parallel 2A3SE amp and similar-better results with mod Eito ST70 running 6BX7 ppp (Eico has bit higher damping factor - probably ~4)

no need for expensive resistors - modern sandcast have little inductance.

have you already built the horn? - does it have a small back chamber? what flare, etc? - will assume woofer with 103 rating is low qes (?)

Freddy