Phono/preamp advice for Rega RP1 needed

I am a starter to the vinyl world and bought a Rega RP1 paired with a Pro-ject Phono Box II recently. I combine them with my home theater system consisting of Pioneer VSX-921 integrated amp and Monitor Audio R270HD speakers, which turns out to be a letdown. I wonder if I'd find instant improvement by hunting some other well-reviewed phono preamp like Cambridge 640P, or I directly go for a higher budget one like Jolida JD9? Or is it mainly due to the lack of musical performance of my VSX-921 and speakers? Many thanks in advance.