What are the differences between the Monolith THX V1 series and the V2 series?

The main difference is that the enclosure was made new from scratch. FEA (Finite Element Analysis) modeling and Klippel laser-based optimization were utilized to create this durable, high-profile surround that's made from a unique formulation of NBR (nitrile butadiene rubber). This formulation was developed after months of modeling and prototyping to ensure the highest levels of excursion, without sacrificing linearity or distortion.
The driver has also been completely redesigned. FEA (Finite Element Analysis) modeling and Klippel laser-based optimizations were used to design a cone that is capable of astounding >80mm peak‑to‑peak excursions. The spider is made from multiple layers of NOMEX with integrated tinsel leads hand-stitched in place for low mass, yet high strength and durability. The purpose of these vents is twofold ‑‑ first, they allow convective airflow to cool the voice coil, and, second, they reduce asymmetrical compliance due to air compression under the cone/spider, which would appear as unwanted distortions.
The frequency response on Extended EQ in the vented mode now can reach a bit deeper than its predecessor.
So to conclude, both versions are great and the V1 has received really good feedback from most of our customers.
But the V2, like all upgraded items, is going to be a better performer in both frequency response on high SPL as well as increased overall cabinet strength and limit unwanted panel vibrations that would cause discoloration and distortion.