So, back to Class D, besides the overpriced GANFET models that are being praised by reviewers with a fair fight comparison with silicon based Purifi Eigentakt models (which are half the price, twice the power, and measure better), don't just settle on Buckeye, Nord Acoustics has a great Eigentakt monoblock with more options and a better build aesthetic.
As for preamps, I do like my Schiit Freya+, so +5 on that one. But I also enjoy my Rogue RP7 which you can attain used in your price range.