KARAJAN: 1960s box and remastered editions

I have just acquired the big DG Karajan box and it highlights a dilemma I find increasingly in the era of multiple reissues. How do you know which remastered version of the recording you are getting?

For example, a while back I saw the Galleria issue of HvK's Beethoven overtures cheap on a resale website and succumbed as I particularly wanted his Consecration of the House. Later I also saw a bargain offer for the HvK Beethoven box and fancied giving the digital symphonies a try. (I had expected marmoreal downgrades compared to the 70's, 60's and 50's sets but was astonished at how good the middle symphonies are.)

Anyway I now have three pressings of all the DG Karajan Beethoven Overtures and they each sound slightly different. I find it difficult to decide which I prefer and would like to know if they are different remasterings or perhaps it's merely a variation in sound volume.