I have the "Boxed" set on CD, which is SQ, and a Surround Master v.3 decoding it. All three sound the same to me. What differences do you hear? I'll give it another listen. As for the CD-4 version being an upmix, where did you hear that? I hadn't.
To make things clearer (or perhaps more complicated), here are some of the notes I've been collecting on all versions of Tubular Bells (I have only transcribed the ones related to Quad):
QV2001 – Quadraphonic version
The first 40,000 copies are not real QUAD, the following ones are. (See Boxed.)
QD13-105 (US Quadra disc CD-4 channel discrete). (is it same mix than the one before?)
VP2001 – Vinyl Picture disc. Stereo remix of the Quadraphonic.
Appears in the Boxed Compilation.
1983 - CDV2001 (First CD edition).
The CD release of the Boxed album contains a stereo remix of the quadraphonic version.
1976 - Boxed
Is a compilation album written and mostly performed by Mike Oldfield, released in 1976. It features SQ system 4 channel quadraphonic remixed versions of his first three albums (Tubular Bells, Hergest Ridge and Ommadawn) and some collaborations.
Boxed features quadraphonic remixed versions of his first three albums. Oldfield later explained that instead of being true 4 channel sound, the initial quad remix of Tubular Bells, released few months after the stereo version, was a "strange fake out-of-phase system", because it was so complex a mix without automation.[1]
The quad remix of Tubular Bells on Boxed was entirely different and true 4 channel sound (later released on SACD). The Boxed-CD version still contains the SQ-encoded quad mixes and plays as normal stereo without a quad decoder. The SQ quad remix Hergest Ridge was the only version of the album available on CD (until the 2010 Mercury Records reissue, Deluxe Edition), as Oldfield disliked the original vinyl mix.
The traditional hornpipe melody "The Sailor's Hornpipe", which was the finale from Tubular Bells, has an extended speech from Viv Stanshall, which is from the recording sessions at The Manor Studio (see Tubular Bells original ending).
Tubular Bells was re-mixed in quad by Phil Newell, assisted by Alan Perkins. Hergest Ridge was re-mixed in quad by Mike Oldfield. Ommadawn was re-mixed in quad by Mike Oldfield and Phil Newell.
2000 - Simon Heyworth remastered the album for an
HDCD release in 2000
2001 – SACD by Simon Heyworth
2.0 of previous remaster + 4.0 Quad mix by Phil Newell de 1974
(Some copies of the previous two were labelled as the "25th Anniversary Edition").