Big post - sorry Thiaman
(But please read and respond)
Not sure I can add much more to what I said already, but I've checked out the deck you have very very briefly - it's kind of old and I've never ever heard it in action - all third hand knowledge. While it's perfectly fine within its context - significantly better than the rubbish you'd likely get on top of your average midi-system - I'm not sure it warrants a significant outlay in an outboard phono-stage. From your original post I get the feeling you thought of the Nad as a stepping stone to check out the water for spending more on a phono stage - and I'm assuming you mean 50 quid or so. My gut feeling says that the 50 quid would be better spent by saving it and waiting a little longer and buying a new record deck - I'm sure that Andrew or Clare would be more than happy to suggest what. I believe the deck that you have originally sold for about 50-100 quid about 30 years ago. That makes it a real record deck, but a budget one.
Maybe... get your phono stage checked out in your local hi-fi shop - don't put it in for service - ask to listen to it with a budget deck (they should certainly be able to set it up correctly!). If the shop is worth spending money at they will indulge you a bit in the hope of future business - if they won't indulge you walk away and find somewhere else. You can help them a bit by trying to turn up off peak of course
But if it turns out there's a problem with the phono stage do not feel pressured to buy something right there and then. A decent shop will even let you take your own (AV) amp in, or provide a similar equivalent to check out some options. You really might find that spending 100-150 quid on a new deck yields greater results than spending it on a phono stage. And it might be worth waiting to save that money up if it's a big deal rather than spending 50 quid on a phono stage right now.
I don't know if all of what I've just said is likely to be what you want to hear. And I may be way off the mark, but I really wouldn't want to see you spend any more of your hard earned cash without getting some worthwhile results. The phono stage in your Yamaha amp will not be the best phono stage in the world for sure, but then unless you've got a seriously high end deck you don't actually need the best phono stage - I run my kind of serious
record deck through the phono stage in my fairly modest integrated amp and while I'm completely sure I could get benefits from a seperate phono stage, I don't think it's even close to my next upgrade.
Andrew? Clare? Others? Please come in and save the original poster if I'm way off the mark. And if I'm not please suggest possible ways he might like to go forward.
Your comments would be welcome I'm sure.