voodooman13,
You have some really nice audio equipment, with one glaring exception. The NAD Miso 5 is a lifestyle 5.1 channel home-theater in a box. It is good quality, for what it is. But it is not of the same relative sound quality of the other hardware in your system and it would be the obvious first choice for replacement. Based on your initial post, I don't see a need for 5.1 HT as you only list 2 speakers (the Vandersteens). If this is the case, you should replace the NAD first, even if you ultimately decide to replace the Vandersteens or add a sub. You NEED quality amplification going forward, and you don't have it currently.
Regarding the muddy/distorted sound you are hearing now, it is likely not the Vandersteen speakers causing this. My guess is that the amplifier is running out of juice, or you have a setup problem with the TT. There would be the more likely causes of muddy/distorted sound.
Hey, it's your money and you can do what you want with it. But if you are trying to get audiophile sound from your system, and you have all audiophile level kit, with one glaring exception, you should probably address that exception first. That exception is the NAD HT/HTIB/lifestyle unit.
Good luck in your quest.