No, the DSS doesn't have an input for mic in. Only the Creative Recon3D and Astro Mixamps have that.
I use a bluetooth clip-on earpiece for chat though, since you can output voice audio to headphones or speakers.

It's a much better alternative IMO because then I don't need to meddle with a long mic.
Sorry, didn't actually saw your post at the top of this page.

All Sennheiser headphones/headsets has a sort of a clamping pressure, kinda like their signature. With that said, different Senn cans has a different clamping pressure.
The PC350 doesn't clamp as tight as the PC330, but I always found the pleather earpads to be uncomfortable on them.

The PC350 has a different sound signature all together in comparison to the PC330. It extends quite well on the mid-bass side, without rolling off into the low-mids. Mids though, given this is a closed headset doesn't sound as forward as I expected it to be. It felt airy and the highs can be a little fatiguing at the same time.

Personally, I never liked the PC350.

As for the amp, it really really depends on the situation. The DX has no headphone amp, but neither the PC330 or PC350 needs an amp to drive them. But the DX's output line is at a stupid high 100ohms output impedence, way too high for the either headsets. Rule of thumb is that output impedence should be 1/8th of a headphone/headset's impedence, although many other exceptions may apply.
For this case, the PC330/350 will probably have some dampening or bass distortion at very high volumes with the DX.

Upgrading to a STX will improve your sound quality, but not by much because the PC330/350 are limited to what they are. They're low-impedance, easy to drive cans with only marginal benefits in amping.

Do you absolutely need to try the PC350 though? As in, do you really only want to have a closed headset? If not, the PC360 is a good alternative choice.
A lot more bass shy than the PC350 however, but the mids are more detailed and the highs aren't as fatiguing. Most importantly, it's much more comfortable than the PC350 IMO.

The downside is that it is an open headset, so sound can leak out and you're not totally isolated from outside noise.

Should have honestly go for a Beyerdynamic DT770 Pro + DX clip on mic
But let us know what you think, you might just like the PC350 since sound and comfort are fairly subjective.