The 8 ohm DeltaLite-2 2512 is a better performer than the original 4 ohm (especially the DeltaLite 1), but this cabinet was developed before the series 2 driver. The 8 ohm version was a -2 type and because of this that are in fact louder in spite of drawing less power from the amp.
The Subway 112 is reasonably compatible with the 8 ohm Scout cabinets, it's not going to be perfect (or as even as 2 x Subway 112's) because the tuning is different. Passive radiator cabinets behaves little differently than ported cabinets because of the mass of the resonant diaphragm versus the air mass in the port.
If yours is the 4 ohm version with the series 1 driver, the first thing to do is to update it with the series 2 version at 8 ohms. Then IF you need to add another cabinet, the Subway will be much more appropriate as a pairing.
Hope this helps.