I use them on my Montis' and they work great. I had to order the bolts with the ML specific thread separately. They will replace the original round rubber feet with attached bolt. So you need the correct thread size GAIA bolt additional to the GAIA 2 feet for it all to fit correctly.
I don't have any personal experience with Amazon Music, but have you looked at this FAQ page already? Amazon.com: Amazon Music HD FAQs: Digital Music. You might find some leads that help you along. Good luck.
I never heard the Theos. But if you would get the PrimaLuna (integrated or power amp), I bet you won't be disappointed. And as soon as you feel comfortable, start tube rolling. As always, if you can audition any gear at home, do so.