It is ver difficult to explain the sonic differences, I preferred the KRC-HR, to me it sounded sweeter and more natural, of course this is only my taste and yours may be different.How it compares to the newer KCT I have no idea as I have never compared the two. I suggest you try to audition these preamps and make your own decision. Most of the suggestions seems to be based on what should sound better because of price or based on reviews which people have read, not on personel experience with the products, which is the only opinion that really is valid.
Mike