I guess there could have been some sonic problems on my VAC Ren mk II, but I also had a VAC Avatar Super, and I would say the overall house sound was the same. Very refined and polite, lots of air were the positives. I think the VAC's were the best high's I've heard from tubed products. Plenty of detail and air, but no sign of grain. Overall I preferred the BAT VK-51SE over the VAC and a CJ Premier 16LS mk II. The CJ and the VAC sounded a bit more 'tubey' with a warmer midrange, and if this is your cup 'o tea, they might be for you.
To date the BAT VK-51SE is still the best preamp I've heard in my home. It was much more dynamic, powerful and lively than the CJ or the VAC. The soundstage is also much larger with the BAT. I've also heard a VK-5i, like yours, and again, the VK-51SE is more dynamic and powerful, but the VK-5i is a bit sweeter in the mid's. IMHO, the VK-5i has the midrange glory of the CJ and the VAC. Of these three, I would say the CJ has the best midrange, the VAC the best highs, and the BAT the best bass. I also still think your BAT would have a bigger soundstage as well.
I sold the VK-51SE for economic reasons, to date, I still haven't heard a better preamp. I've heard preamps that better it in certain areas, but not as a whole.
That being said, I do hope to hear a ARC Ref 3 someday, as I've heard many great things about this preamp.