Technically, the Soundblaster is a DAC and amplifier. Anything that can play digital audio must have some sort of DAC and some sort of amplifier.

I’ve had a good experience lately with Steel Series Sonar software. I use a Syba Sonic and mix of IEMs and Sennheiser HD560S, depending on my mood. Sonar lets me set whatever EQ I want.

I think the sound card functions as a dac already, not sure if it’s an amp, but the pc38x has low impedance and high sensitivity which makes it easy to drive and probably doesn’t need a dedicated external amp. I’m confused when you say the audio is too low but when you increase the volume knob, it becomes too loud so driving isn’t an issue, just find a healthy middle ground by slowly adjusting both while listening to some songs.

Regarding sound quality itself, this becomes a lot more subjective. Try to set your sbx profile to something neutral or turned off first, then go from there. In general as long as there’s no obvious crackling, distorted sound or channel imbalance where one side is louder than the other side (unless the song itself does that), that means it’s working fine. You would have to describe in better detail what makes you think the “audio sound bad”. Does it lack bass? Voices sound muffled? High end notes too strong or too weak? All of these are less of the headphones being broken and more of headphones having their own sound (frequency response). PC38x is rather neutral with the bass mostly flat and rolled off, while a lot of gaming headsets have boosted bass so a person who likes bass may dislike the pc38x because of it.

Next is mostly subjective, what kind of songs do you listen to? People who like hiphop and rnb usually enjoy bass while other genres like classical may not care as much about it. Individual preference matters a lot here. Here you can start experimenting with your Sbx or eq software, just grab some of your favorite songs and A-B listen to them with certain profiles on or off. EQ isn’t inherently bad, sometimes you have a headphone you enjoy but just wish it had more oomph in some places so you start using EQ. If you don’t want to use EQ that’s also fine, try the headphones with the eq/sbx settings at neutral or off for a week or 2 and you might get used to it. I started using an open back this year and going back to my old headsets, I felt they are now too bassy when previously I was fine with them.