From my experiences with the ZH270, it does sound best with an active preamp. I think solid state or tubes comes down to personal preference, as long as its high quality and musical it should sound great. Without a preamp the ZH270 sounds very open and detailed but lacks some of the weight and musicality that only a good preamp can add.
Some preamps that I have personally used with great results are: Berning P-1 (tube), Berning MicroZotl (tube, modified for use as a linestage), Blue Circle BC 21 (tube), Adcom GFP 750 (solid state) and Threshold FET 10 (solid state). My favorites would be the Micro Zotl and the BC 21.
Both of those preamps added all the weight, dimension, and musicality that was missing. I do love the characteristics of the 6SN7 tubes and they mated very well with the ZH270.
Some preamps that I have personally used with great results are: Berning P-1 (tube), Berning MicroZotl (tube, modified for use as a linestage), Blue Circle BC 21 (tube), Adcom GFP 750 (solid state) and Threshold FET 10 (solid state). My favorites would be the Micro Zotl and the BC 21.
Both of those preamps added all the weight, dimension, and musicality that was missing. I do love the characteristics of the 6SN7 tubes and they mated very well with the ZH270.