maybe the splawn/duncan combo just works.
Having heard the Splawn/Bare Knuckles combo with more pickups than most people, I can tell you that it really works well. It is a bit bright and Irish Tours are a bright pickup too, but the Splawn does have working tone controls - it isn't a Marshall!
I guess if your ears are telling you that SD's are better that is what you should use, but having done comparisions of BK to just about every other pickup maker, the current SD production range doesn't do it for me!
I have lots of other makes in guitars (including the dreaded EMG!), but I really can hear the difference with the BK's. I did buy SD basslines for TO's bass player, but the new bass has a Music Man pickup and BK doesn't make one of those. My Jazz bass will have BK's and my Precision never sounded as good as when I swaped out the pickup for a BK.
I am really surprised that you couldn't get a good sound from a VHII/Splawn combo, as I have never heard TO get a bad sound from his.