So the SI 24 has 7.7 liters of displacement (1 way xmax) at the cost of $800 or $104/liter
The Si 18 has 2.7 liters of displacement (1way xmax) at the cost of $162 or $85/liter
I know that D4s aren't available, so think back to when they were, but for less money, why not get 3x Si18 and wire D4 in series/ then parallel them for 2.7 ohms, or even 4x and series parallel D2s for 4 ohms (which are available)
Still cheaper, more displacement, I think similar sealed volumes and less thermal compression on the VCs.
Is there something special about the 24's vs the 18s (or 15's for that matter) besides shear size (which, I'll grant you, is pretty ****ing amazing and awe inspiring lol)