If by "grey sleeved ones" you mean the European Region 2 PAL versions, I couldn't tell you, Nick. I never bought any of those, as they won't play on my American NTSC equipment.
However, I remember reading complaints about the audio on those. I notice that UMG has gone to great lengths to advertise that the AMAHM Trilogy in its new box set has been "remastered" in LPCM uncompressed stereo. That might just mean that they are now offering the same quality that we always had in those black box editions here in the States.