I have found the result is improved by EQ'ing. Not by "seasoning to taste", but by using a spectrum analyzer to measure the frequency response at the listening position, and correcting this with an inverse curve in the Pianoteq EQ panel. I use actively-driven near-field monitoring speakers at approximately ear-level. The improvement to my ears is such at at an EQ'd listening position, the sound is open and transparent across the keyboard, with no emphasis or deficiency in any register. It makes me wonder what equipment reviewers have used, and whether their adverse comments reflect the sound card, speakers, room, etc they used, rather than Pianoteq itself. In fact I myself was somewhat critical of the sound of Pianoteq on first aquaintance, before EQ-ing the replay equipment. But now that I have done that I can say that no way am I interested in using any sample library (with their A/D converter distortions, etc which I am acutely sensitive to).
For myself, I have no problem with the in-built reverb. I admit I am in no way an expert on reverb technology or the hardware/software that is available. But I have heard some truly bad VSTi reverb plug-ins, and in comparison I find the Pianoteq presets neither aggressive nor offensive, if understated.
Regarding EQ-ing, I am a bit surprised that you find the sound improved by a "downstream" plug-in. I take it you are referring to the sound of Pianoteq used on its own? I have the view that the less processing that needs to be done to a sound the better. In this respect I note that the Pianoteq documentation states An equalizer, working in pre-processing (modifying the model before computing the sound). I envisage what this means is that the amplitudes of the individual waveforms used to create the sound are adjusted according to the specified EQ curve before the summing process occurs, i.e. before the "engine" computes the output from the user's input. If so, then you are really getting EQ for free, at least in terms of adverse effect on the quality of the sound. If that is correct, then Pianoteq's EQ cannot be degrading the sound - in any way at all. I do not know what the limit is on the number of EQ shaping points one can have, but by using the entryfield facility one can specify the amplitude and the frequency of the control points very precisely.
As for anything else, I find Pianoteq so awesome I am still gathering my thoughts...