B&W 805 Nautilus for PC?

Did you measure the response?

The sonic contribution from electronics is usually quite small compared to speakers. Therefore, changing that is unlikely to change the sound very much (unless you are using your computer’s internal soundcard/DAC - they are often terrible).
However, there are a few things that may help. The first is that the tweeter should be at ear level, and as exactly as possible. I use Harbeth P3ESRs desktop speakers and lifted them a bit from my desk, for proper response. In addition, I was suffering from a boomy bass due to the proximity of the desk, and raising the speakers made quite a difference. Second, if, as I did, you still find they are too boomy/muffled, and if you are using a Windows computer as a source, you may use the Equalizer Apo software to tame the bass. I measured the response with REW, and created an equalization file to reduce some bass peaks. I downloaded that into Equalizer Apo and it did clean up the sound. Good luck.

Ignore the distractions here. Find out if the tweeters are working to find out if there is too little high or too much low, see what the speakers do in a different position, on tall stools and away from walls and surfaces, measure the response in that position and on your desk, and take it from there. In short, find the facts.

For measurement the best option is the free REW software and a calibrated microphone like the UMIK-1. That does not need to cost an arm and a leg. REW is not particularly user friendly, so you will have to spend a bit of time. If, as I suspect in a home office, you are using a computer as a source, you can equalize in software. And of course, when you are at it, you can also measure the system in the family room. If you are not using a computer there, you would need a mini dsp. Avoid equalizing above about 150-250 Hz.

I meant, avoid equalizing above 150-250 Hz (i.e. the so called Schroder frequeency) for peaks (due to room modes).
In addiiton, however, you can also use the Equalizer Apo as a traditional tone control or even better as an imitation of the old Quad tilt control to change the tonal character by lifting or reducing the response over a longer part of the frequency response.

Sorry for the typos. I was in a hurry to be in time for a meeting.