While no one in the British music industry knows for sure and The Orb don't speak about the topic, I strongly believe it was them, and I'm going to prove it.....
* The Orb's output ceased during 1993-94, when the mixes were created.
* The Orb's debut album, out by this point, had clear Floyd references - a track called "Back Side of the Moon", and Battersea Power Station (made famous by the 'Animals' sleeve) on its cover.
* The KLF, which featured Orb founding member Jimmy Cauty, were also Floyd fans - the cover of 'Chill Out' was a nondescript photo of sheep in a field, meant as a nod to 'Atom Heart Mother'.
* Pieces of 'Chill Out' appear in many places throughout the mixes, most recognizably in the "Dogs" remix, which heavily samples the track "Wichita Lineman Was A Song I Once Heard."
* Not long after the remixes emerged, Richard Wright had the Orb create an authorized Trance Remixes EP for his solo album 'Broken China'.
* In 2010, the Orb put out their album 'Metallic Spheres', the entirely of which features David Gilmour adding Floydian guitar licks over their ambient music. Not surprisingly, this album sounds a hell of a lot like the Trance Remixes.
* The idea that the Orb were behind the mixes formed immediately upon their release (Andy Mabbett's "Complete Guide to Pink Floyd" was published in 1994, and even then, he referenced their 'Orb-like' quality). Many listeners who recognize the Orb's work, including members of the English music industry, consider the discs to be Orb creations without question.
* Considering that the Orb were still fairly new in 1993-94, for another DJ to so accurately capture their unique styles (for example, reverb-swamped TV clips and sound effects floating amongst the ambient noise) in such a short time is unreasonable.
* The first track on the earliest Trance Remix CD, which would be part 1 of "Shine On You Crazy Diamond", is based around a deconstruction of the Orb's own hit "Little Fluffy Clouds".
** Likewise, part 2 of "Shine On" samples 'Chill Out'.
* Given the general dislike towards the mixes (thanks to the 'Floyd is perfect' obsessives), and the Orb's high reputation amongst trance music, one would think they'd deny having created them if they didn't, at least to save face. They've never denied involvement, and inversely, won't flat out confirm it either. As the mixes were unauthorized, this could simply be for legal reasons - and the Orb are known to remain silent on the topic of using samples without permission.
Ironically enough, shortly after compiling this list, I picked an Orb song at random from YouTube - "A Huge Ever-Growing Pulsating Brain", which happened to sample both the signature four-note guitar lick from "Shine On You Crazy Diamond" and (it seems) the opening ping from "Echoes." More Pink Floyd connections.
On the whole though, I've been listening to the Orb's better known music such as "Blue Room" quite a bit to try and justify this list, and after examining their mixing styles, motifs and gimmicks, have no doubt that they were indeed behind the Trance Remixes.
Since there are a number of different Floyd remix CD's out there, I thought I would clarify which ones the Orb absolutely did *not* do.
* 'Absolutely Ambient' -
** Since originally creating this post, I located back cover artwork for this album. Credits are given to 'The Stingman' (technical and creative know-how) and 'The Attitude Brothers' (executive producers).
* 'Welcome To The Remix' - This is an odd CD, later re-released with considerably less cheesy artwork as 'Mixed In The Moon'. Though it includes two of the remixes from the 'Wish You Were Here' disc, the other material was more than likely not created by the Orb, but at least one other professional DJ - who, judging from the 'Megamix 21' track, had admirable talent. Other than a re-edited copy of the 1981 "Money" remake, a lengthy trance remix of "Another Brick In The Wall" debuts here, oddly split into two tracks. While entertaining and well done, there aren't any telltale Orb trademarks that allow me to suggest it may have been theirs.
* 'A Collection Of Great Trance Remixes' - Released after the main series had been completed, this German disc (complete with a grammatically-strange cover) seems to be a third party attempt to construct the 'Great Dance Songs' album using previously released tracks from the Trance Remix CD's, as well as the mysterious "Another Brick In The Wall" from 'Welcome To The Remix'. Not surprisingly, the 'Wall' remix sticks out like a sore thumb.
* 'Piper At The Gates Of Dawn Trance Remixes', 'More Trance Remixes', 'The Final Cut Trance Remixes' - These discs are often lumped together with the main series, and they shouldn't be. Released five years after the main series, they have nothing at all in common stylistically with the Limited Edition Trance Remix discs, and were actually the homemade efforts of a teen Floyd fan named Alex Wroten, who put them together to the best of his limited audio-editing abilities. The existence of a 'Piper' disc is actually a fairly new revelation; due to eBay sellers cashing in with poor copies of his other two discs, the 'Piper' set took over a decade to reach the public. (Alex also created a 'Saucerful Of Secrets' disc, but this was lost in the midst of computer troubles.)
* 'Floydhead: The Floydian Propulsion Project' - Of course, this was a strictly fan-made project, created by individuals named Seth, Ste-V, Michael Alan, Jimmy Rad, and Hainkm. (Unlike anything else mentioned on this page, this disc is actually available commercially through venues such as Amazon... quite odd, given the actual Pink Floyd material included.)
* The Beatles - 'Sgt. Pepper Trance Remixes', 'Day Tripping: Magical Mystery Tour Remixed', Led Zeppelin - 'Coded: Limited Edition Trance Remix" - These three bootlegs were the work of an individual named Nasty Little Dog, and released on a label called Chelsea Records. Clearly meant to mimic the Pink Floyd discs (note his use of "Limited Edition Trance Remix" to make it seem as though they were related), they are......... well, for lack of a better term, shit. Utter, utter shit. Aside from poor quality rarities from the artists used to pad out the length of the discs (including a couple Beatles outfakes), the remixes themselves are as amateur as they come - playing "I Am The Walrus" in its entirety twice with a ridiculous amount of reverb piled on, for instance. It goes without saying that the Orb had nothing to do with Nasty Little Dog.