I have a pair of Quest Zs powered by a Krell KAV250 & experienced the sound problems as you. I put a Sonic Frontiers Line1 which really helped flesh out the sound but it still got a little bright on the top end so I tried a Pair of cardas quadlink 5c & got a really mellow sound.I have since traded up to a Line3 & Resolution REference cables all around & get a fabulous sound.Try to borrow a tube preamp & you might be very surprised.Should you decide to go in that direction it will be a lot less expensive.The sound problems you have may partially caused by the Wadia & a preamp will really make a difference. I am partial to Sonic Frontiers gear because it is sonically neutral.Good luck.
