Sound traps/acoustic panels to improve the sound

I need advice:

I have open-baffle Concentus Lyra speakers manufactured by Nightingale (Italy). They had marvelous sound, especially with jazz, but when I moved to a new flat, I was aware that they lack HF extension as if covered with a blanket. The amp is Cary SLI-80 (the other amp is the older SLI-50). They are positioned against the short wall opposite the balcony and placed nearly in the middle of the room.
The manufacturer had told me before that these speakers do not require any specific placement or room treatment.
My question is: should I look for any sound traps/acoustic panels or other room tweaks to improve the sound? I have other speakers on loan now (the cheapest Montana DPS speakers) and they sound very balanced, though do not reproduce jazz music as well as the former speakers. With the former speakers, I was surprised to hear the cymbals when I moved close to them (to high frequency drivers), while I don't hear them from my listening spot (which is not the case with Montana - I can hear everything from my listening spot).
I will appreciate all thoughts and recommendations.