Before you start switching cables and/or speakers and spending hundreds of pounds in the process, I would suggest you google "room acoustics", or seach these forumm for discussions on this important topic. "Neutral" speakers could sound "forward" and "bright" speakers could sound "harsh" and fatiguing" in a sparsely furnished room with bare wooden floors and full of hard and straight surfaces; and "warm" speakers could sound too bassy in a heavily furnished room with thick carpets, lots of cushions, big sofas, thick curtains. (Speaker positioning could also make a drastic difference to the bass but not so much to the treble).
I would hazard a guess that your listening room is the former kind and you may find that slightly changing the layout of your room to remove reflecting surfaces which direct the treble to the listening position (high/mid frequencies are is more "directional" than bass frequencies), and/or adding soft furnishings like a big rug, some cushions, table cloth(!) and plants (all for less than £100) could make the difference that you desire, or improve it to the extent that you achieve your goal by also changing to copper speaker wires.
I speak from experience as the above was exactly what I did to my Cyrus/Spendor system (see my signature) in one afternoon without changing source, amp or speakers and the result was exactly what I had wanted.
Have fun!