I have heard matching, tower based 5.1 systems on a couple of occasions and they are universally spectacular. Given that the ergonomics/logistics work, it is undoubtedly the best way to go. That being said, most multi-purpose rooms can't accommodate a system of that size. The Maestro and Waltz were created to satisfy the needs of the average room, without to great of a compromise to sound.
In your room, because of door/window configuration, wall-mounted Waltz will be better than corner-positioned Bach/Mozart. This not because the Bach/Mozart are not better speakers, which they are, but because the corner is generally an awful place to put a speaker. Speaker position will have a more dramatic impact on sound. So much so that 5 identical speakers can be made to sound completely dissimilar.
So that you understand the logic behind the design of the Maestro, spider-cone woofers were chosen to increase its dynamic/output capability while maintaining a compact, horizontal cabinet. Through careful driver/crossover tuning, Maestro is voice matched to Mozart/Baby Grand/Concert Grand.
The Waltz is even more interesting. Normally drivers are designed first, then cabinet, and then crossover. With Waltz and Schonberg series, this approach does not work because cabinet volume/dimension is essentially predetermined. To make the highest quality sound, drivers and crossovers are developed simultaneously. This is why Waltz can handle so much power, while delivering an expansive, detailed and dynamic sound, without compression.
For your dedicated system, I'd recommend bypassing 6.1 and moving directly to 7.1. The former does not really exist in the pro world any more, so any array larger than 5.1 is being done in 7.1. If this is your ultimate goal, I'd do three pairs of matching or mixed Vienna towers with the Maestro center.