Permanent solos over Spiros (solo B, mitt E) were brighter and tighter than all Spiros (solos with mitt E) tuned AEBE? And now you're playing the same Permanent solos over Spiro solo B and mitt E, tuned GDAE - and you find the Permanents to give you better clarity?
Yes, exactly that. This happened over the pandemic while I committed myself to tackling some Bach cello suites. I actually DID want to try to get some of that sound and I thought I might as well try the exact set up and see what I find. I think it did help me a little to at least feel what Edgar or Paul might be feeling as they play. I spoke with Paul quite a bit during this time and we discussed the set up and the challenges of playing the suites.
The biggest change is playing solo strings in solo tuning. You quickly realize some of the reasons why they get that sound when you venture into that territory. Of course, it's all in their bowing and their hands (and intellect) more than any other factor.
I am NOT a fan of Obligatos in any form. I find that they roll under the bow and generally do not feel good in my hands. If I was going that route I would probably go with Bel Cantos but I haven't played anything with a perlon core for many years. I've known Paul casually for a few years but have only really heard him play once in person. I've seen Edgar a few times but have never had the pleasure to meet him. They are both truly wizards.