Gerryn, with the MaxxHorn Immersion's 100dB/8Ohms sensitivity, it may only be able to use the first watt or two of your VAC monoblocks; but just like any other high-efficiency speaker, the MaxxHorn will sound more powerful with high-power amplifications. The more important concern is whether the amplifier using a myriad of tubes is of a design ingenious enough to produce the same level of spectral uniformity and microdynamics as that using a single 300B.
From your profile, I can also see you are using a multi-driver speaker system. If you are familiar with speakers featuring a single-driver, then I assume you already have a frame of reference. If not, the MaxxHorn will be very different-sounding than what you have ever experienced.
In-home audition is almost akin to reviewing equipment, the advantage being the absence of obligation to write. If you don't mind uncrating and crating the MaxxHorn, I would urge you to try it. You are also welcome to check out what I found in the following review on MaxxHorn Immersion:
http://www.dagogo.com/MaxxHornImmersion.html
Hope this helps.
Constantine