At this moment, I think the GS-1 is better or at least quite in the same place of the Soloist, however I may be wrong, I never heard 'em.
That Apex Peak, can you talk a little bit about it? Do you recommend the Volcano power suply for it as well?
Is the GS-X better than all those amps? I mean, the GS-X just lose to what? Liquid Glass and those hell expensive ones?
Soloist and the GS line share a very similar circuit. You wouldn't be too far off the mark saying Burson's new understanding was finding the HeadWize article on the dynalo ;)
I only heard the Peak with the Volcano so no idea what it adds. Peak has the advantage of the tube input to tune the tonal balance. I loved it but didn't want to deal with tubes anymore.
GS-X mk2 is the best head-amp/pre-amp commercially available... period. When looking at Cavalli gear, take $2K-5K off the top to see the real value :P They are priced based on selling very few units. Where the GS-X mk2 is inexpensive for what it is because HeadAmp has sold hundreds of them over the years.