Assuming you are looking at $1500-$2000 used range, I would recommend the Allnic H1201, or a Herron VTPH-1 MC+.
04-16-15: ShawnlhI was just about to post the following when ZD and George beat me to it:
I'm surprised that everyone [other than ZD and George] has been offering recommendations without knowing what the cartridge is, and what the integrated amp (or preamp) is.
Some preamps and integrated amps, especially some solid state models, will have input impedances that are too low to be driven in an optimal manner by some phono stages, especially some tube-based models. And obviously the choice of an optimal phono stage in a given price range may hinge on the output level and loading requirements of the particular cartridge.
For example the output impedance of the Decware ZP3 that is apparently being considered by the OP is spec'd at "less than 1K." That is presumably at mid-range frequencies such as 1 kHz. I'd expect that the unit has a coupling capacitor at its output, which could very possibly result in that output impedance rising to 3K or 4K at frequencies approaching 20 Hz, resulting in significant deep bass rolloff if the preamp or integrated amp's input impedance is less than 25 or 30K or so.
Also, as the OP no doubt realizes, the ZP3 needs an external step-up transformer, such as one of those offered by Decware, to be usable with LOMC cartridges.
04-18-15: ViridianTrue enough, Marty, but note that the OP states "I have changed my amp and cart." And posts from 2011 in his system description thread refer to the MF A5. So apparently it has been replaced with something else.