In terms of changing tubes, I would be extremely hesitant. Here is what ifi concluded: From a purely technical side, GE JAN 5670 NOS valves are the best ones we could find in large batches enough to be commercial. 1. Excellent consistency of electron valves between batches 2. Glass is thicker than usual, 3. Controlled warm-up 4. Tight specifications on grid current, 5. Low noise and microphonics and exceptional longevity And since genuine military grade New Old Stock 5670 electron valves are reasonably well available (unlike many desirable electron valves), it'd be a shame not to exploit their potential. Hence we exploit as much as we can, fully aware of what GE JAN 5670 NOS performs and sounds like. At iFi Audio we always strive to find the best parts for tasks given. This is not lip service – we ruddy well mean it! We experiment with lots of components from a number of manufacturers, measure, audition and once extensive research is gathered, we cherry-pick. If every component’s related decision would be as simple as it was with GE JAN 5670 NOS, our engineering lives would be much easier and we’d spend a lot more time in the pub! In conclusion, this electron valve has an incredible price-to-performance ratio, it honestly doesn't get much better than this. We've been there, we've done that – we’ve got the t-shirt and the blinking key ring. You're of course free to experiment with our Pro iCAN past warranty period. But it's highly unlikely that you'll find anything better for sane money. Please trust us on this one; our Skin, she does not joke around when it comes to sound quality. (I own the ifi Pro iDSD and Pro iCAN).