Parasound Zpre3 mismatch?

I purchased a new Zpre3 to finish an inexpensive craft room system. I paired it with an Acurus A250 amp and "vintage" Infinity Reference 5’s with the Emit-R tweeters. The miss and highs are there and very present, almost clinically so. However, the low end is almost non-existent. Even when I crank the bass, it helps, but minimally. My first thought was an issue with the amp. I was previously driving the speakers with an old Proton integrated amp. It also has a pre-out, so I plugged it in to the Acurus and everything sounded great. Any thoughts on why the Parasound sounds so terrible in this combination? Thinking about trying a couple other pres. Maybe an Adcom GFP-815 or Vincent SA-31.