The cover artist says thank you! And so do I :)
Part of the soothingness you're referring to might have to do with my cutting out of some rather aggressive high frequencies from almost all the percussion. It just sounded better to me to do that. Maybe because the synths have nice warm mid-lows. Otherwise I have to thank the libraries for the tone.
The lead at 1:15 in Digital Summer is a combo of strings and electric guitar. My favorite part too :)