@ cradle emperor
Your SRH240 and Senn CX300s don't need an amp. I've owned the SRH 840 and 940 and they can be driven OK without amping. I also had the CX300 for a while earlier on. As you go higher (with the Shures) - there can be some benefits - but the with the SRH240 you're not going to see a lot. I'm not sure regarding the B&O A8 - never heard them - not sure how sensitive they are. How are they now with your iPod?
Regarding the buds you're looking at buying. Haven't heard the PK3 - but CEE TEE used to own them, and I trust his comments. He says they don't need amping (higher versions will do). So in interim - for your portable listening - you don't actually need an amp. If you want one to experiment with - I can recommend the E11 (form factor is great, and it will drive a lot of higher cans). I've even used it with my HD600 and it goes pretty well. Most of the time with my portable listening (if you are actually out and about), I find an amp is more hassle than it's worth (bulky). Transportable is a different story.
Your computer though is a different beast. If you are getting static and noise - then you'll want a DAC.
My personal opinion - and I'm being blunt here. By the looks of things, most of you gear is very entry level. You're unlikely to need 24/96 or indeed and of the coax etc inputs. I can't see the point in you spending $150+ on a dac/amp as a first buy - when most of your gear doesn't warrant it. If you're trying to future proof - then maybe see the point .... but not what I'd do.
I see 2 possible options. E10 for your computer - low priced, reviews are good, small footprint. Not portable though (ie PC/laptop only). I haven't heard it - just going on reviews. Check with someone who has owned it - there are quite a few that have it now on head-fi. If you get the E10, I honestly wouldn't worry about getting anything else for now - until you significantly upgrade your headphones. When you reach that stage, get something that will suit the cans you're going to buy.
2nd option - just get the E7. Yes it's only 16/44 - but it has a decent DAC and you're not trying to drive anything really difficult. It is very cheap and will give you an entry point that can be used both portably and with your PC. No sense blowing a lot on gear only to find out that the 'night and day' difference you see on Head-fi is in reality quite small. For reference I own the E11, have previously owned the E7 and E9. Rest of my gear is either in my sig or in my profile.
If you were really going to spend a couple of hundred on upgrades (ie new buds + thinking about E17), you would be far better buying a decent head-phone like the HM5 and then getting the E10 for your computer.