VP150 is sealed. M2s have ports (as CatBrat already mentioned).
If I had a VP150 taking up space I would be more tempted to try making a single "M2 in a big cabinet". You could probably use the unmodified VP150 cabinet on one side and make something similarly-sized for the other side.
The M40 (basically an M3 tuned down real low) has remarkably smooth bass... I always wondered how one or two 5-1/2" woofers would work with similar tuning.