I like Drumm's early stuff best (the two untitled records and the Triangles album, for instance), but they're also far from ambient. Seems some of his recent Bandcamp works might be less "intense" than Imperial Distortion and could suit OP's query ?
Anything from Ultimae Records. The Fahrenheit Project compilations would be a good place to start. Ultimae
Haven't heard those recent works. Might have to check them out. I think the most recent thing I have is the Tannenbaum 2xCD.
Those liking the more drifty floaty ambient stuff could do worse than start exploring European choral music from the 12th century to the 16th century. Yes, this is all religious, but mostly 'cos the church had the money to pay composers and choirs one way or the other. However, if you don't have the Latin you won't know and even if you do by the time you get to Thomas Tallis and the likes of his Spem in Alium you really won't know, 'cos Tallis was using voices at least as much as instruments as conveyors of words and meaning. A good starting point (if it is still in print) might be something like Leonin - Perotin, Sacred Music from Notre-Dame Cathedral by Tonus Pergrinus on Naxos, or The Tallis Scholars' most excellent disc of Allegri's Miserere, Mundy's Vox Patris Caelestis and Palestrina's Missa Papae Marcelli.
Stars of the Lid - And their refinement of the decline and everything by SOTL Biosphere/Deathprod - Nordheim Tranformed White Lunar - Fim Music by Cave/Ellis very mellow Love The Orb particularly Live 93 and Adventures Beyond the Ultraworld Future Sound of London - Lifeforms
Don´t forget the germans. They made some amazing music in the 70ties. Ash ra temple, Cluster, Harmonia, Tangerine dream just to mention a few.
Along these lines, I can't recommend Cluster & Eno and the After the Fire album credited to Eno, Moebius and Roedelius highly enough. Both of these are essential listening as far as I'm concerned!
Hammock - 2010- Chasing after shadows..........Living with the Ghosts. double cd.....filling the house right now.....if you like ambient..you'll certainly like this...heard about this group from a person who is really into this type of thing.....subtle and beautiful.....Haunting guitar work....lovely.
I will recommend this album and artist in any thread I possibly can. I especially love his first album (though it gets better after the first track): Pepe Maina - Il canto dell'arpa e del flauto
Probably more in the post-rock category for most people. One of the loudest bands I've ever seen too...had to leave during the encore it was so unbearable.
Constellation Tatsu is a fantastic cassette label out of Oakland, CA, that puts out "batches" of three or four releases every new season. Any fans of Eno, Stars of the Lid, the Krautrocky end of ambient, should snoop around there. Some of my favorites: Les Halles Hakobune Daniel Klag
Go listen to the version of Like Herod on Government Commissions (the album taken from their BBC sessions)...And wait for the quiet tinkly stuff to stop...It's a pause while the whole band turn EVERYTHING up to 13...Then your living room will be destroyed... Or pretty much anything on Mr Beast or Hawk...which are more their hard rock albums. As someone else noted, live they were sodding loud...
Wow lots of interest in ambient music in the past couple of weeks posts, I've spent four hours sifting thru the recommendations. My preferences are German electronic music from the 60s & 70s because they had to work really hard to get their sound. For Eno I prefer his collaborations (Cluster and Hyde) and his work as a producer (Talking Heads) to much of his own music. I also gravitate to the early synthesizer experiments and Ciani's Lixiviation (Buchla) and Spiegel's Expanding Universe are new to me and worth pursuing. The Giles Reaves albums are also worth investigating if you like 'new age' ambiant. Of the newer works Gas' Pop has an entirely distinctive sound and I'll investigate their other albums. One my finds from a couple of years ago was Method Music by Lawrence Ball and Pete Townshend (yes, from The Who) a really exciting development in music. And a round of applause goes to The Orb's Alex Paterson for releasing Chill Out World before The KLF release of the Chill Out anniversary edition, smart move! Enjoy!!