I have 9011 but always interested in learning from fellow MBL 101 owners their experience of different amps. In general, I am wary of tube amps. I have ARC Ref 40 and Ref 10 before. Both sound greats in the beginning but performance goes downhill very quickly due to tubes ageing. I have now Passlabs Xs. It is great and very happy with it.
That's great that you are happy and in the end what it's all about, what size of room do you have? What type of music do you listen too? Are you into analogue.
I have never owned the ARC Ref40 or 10 so I can't comment but back when I was doing amp evaluations I owned MBL 6010d, Arc Ref3, VTL for some three years plus and VAC. I never had any issues as you mention, VAC was my favorite out of the others.
Have you had the 6010d paired up with your 9011's? What cables are you using?
Have you checked out my thread about my VAC journey? If not you should, prior to leaving and upon arrival back I had the 9011's paired up with my 101E's.
Any pics you can post showing your set-up.