I am curious what Opeth DVD-A and/or BD you are referencing as I thought Steven never did any surround for Opeth.
I never heard of the Japanese mini-lps before and now I need to pretend I never did because they don't look all that affordable to start trying to collect. I believe I have the DVD-A/BD for all of the Porcupine Tree and Steven Wilson releases. I wish they would do just BD releases for the Tull as I don't want to buy the boxsets just for the BD, and now most are just coming with DVDs which is disappointing.
Sorry for the delay, I saw some othe people answered to this question. Beside that, I think SW got involved in the production an stereo mixing of some other Opeth's albums, I can't remember what of them now. And Bruce Soord did some other 5.1 remixes. For me Opeth is one of those bands you will always be able to find quality in any of the records.
About Jethro Tull, I suppose that when SW began to remix their albums, BD-Audios weren't so popular as they are nowadays and they decided to keep the same book format for all of them. Something similar with King Crimson and the DVD-Audios production.
And about the mini-lp editions I recognize it's more a freaky collector hobby than a sound matter. I think they're really nice. The first albums I bought from Porcupine Tree were their DVD-Audio, from Stupind Dream to Fear Of A Blank Planet, but I wanted their first albums too so I decided to buy the Japanese editions because I could find them not too expensive at Ebay and almost all of them had extra tracks and bonus CDs. Once I had all of them, some reissues of their DVD-Audio were published (IEZP-54/58), they were cheaper than first editions (IEZP-7/11) and the Euro/Yen exchange was really good at that time. I only had the DVD-Audio editions, not the CDs, So I decided to make me a Christmas present.