If I put my headphones, which are 32 ohms in a desktop amplifier will the sound quality be better compared to when I plug it directly into my computer or phone? Or will the quality be (about) the same?
That depends on a lot of factors.
1. The output impedance of whatever you've been using it with. If the output impedance is high it can EQ the sound - either making the bass sound like a tidal wave of molasses or a tin can with a background burble of boiling molasses. Putting an amp on it that doesn't have this problem nor any other distortion issue can give the headphone more precise bass, but as to whether that's better for you (ie you might prefer the tidal wave of molasses, even if it's full of distortion) is something we can't answer either.
2. Whether the sensitivity/efficiency of the headphone is getting a lot of distortion out of the amp at your listening level. If you don't listen loud enough (which is hard to determine unless you have a dummy head set up to check if you can listen at 85dB average) then you don't need a lot of power unless you're using very low efficiency headphones. And even if it's cleaner as you play louder, it becomes a question of whether you can tell the difference or how much louder you're listening on average and whether that's safe or, if you can control yourself from cranking it up all the time, whether it's worth it for you to not be able to use that all the time (kind of like whether it's worth it to you to spend $5,000 on a turbo kit for your car if you can only really use it on weekdays).
The amplifier has a headphone output and is buying an amplifier worth it if the headphones are 32 ohms?
Impedance isn't really the key factor here unless your computer or phone have a very high output impedance (ie, #1 above) which can be made worse by other distortion if not clipping as you push it hard (#2 above). If you're only dealing with both of those problems then the difference can be more noticeable. Otherwise, hard to tell unless somebody else has exactly the same equipment, and even then, it's a question of whether
you can tell the difference, much less if the expense was worth it.
I have the Philips Shl3300 and I might buy Edifier H850.
It would be easier to answer if it was about known very hard to drive headphones but in your case, not really. Philips states 108dB/1mW and assuming that's accurate (ie it's not actually 108dB/1
volt) which is higher than some IEMs (though they still have the advantage in isolation) and assuming Edifier's "Sound Pressure Level" spec of 96dB is actually sensitivity, ie, 96dB/1mW, that puts it near the sensitivity of the HD600, but with a lot less need for the amp to produce voltage at the Sennheiser's 300ohm impedance.
Basically, your soundcard and phone have to really suck for an amp to have a lot of improvement on the Philips, and to a lesser extent, the Edifier.
