If you are still planning to use the Harman Karman HK990, I wouldn't bother to go with a separate phono stage. Your 990 has a built in phono stage, correct? Just enjoy it until you are ready for a full electronics upgrade.
If you desire an upgrade, I would look for another integrated amp with built in phono stage and upgrade that way. Maybe an integrated amp from Ayre, Plinius, Belles, Krell, or BAT would probably be a significant upgrade over the HK. YMMV.
If you desire an upgrade, I would look for another integrated amp with built in phono stage and upgrade that way. Maybe an integrated amp from Ayre, Plinius, Belles, Krell, or BAT would probably be a significant upgrade over the HK. YMMV.