have a bit of patience.
do realize that we are not paid and respond here in our free time.
1. you can use a soundcard with a laptop. they make external soundcards you know. the xonar u3 is small, portable and has dolby headphone. i believe the larger xonar u5/u7 or creative omni might have virtual as well but you would need to check.
2. amplifiers have nothing to do with virtual surround. the dac (digital to analog converter) and associated electronics/software/drivers (depending on if its a hardware or software based system) do this. any headphone amp that is only an amp will just amplify the signal. most external headphone dac are also stereo only. the only products which defy this are external soundcards, specialty products like the mixamp/dss2 (both of which have their own problems) or using razers free virtual surround sound program running on your pc with an external headphone dac as well (i've heard it works but due to my setup i can not test this).
3. if you do not like the ad- lineup headband the akg q701 perhaps though they are more expensive, and harder to drive so need a good amp. not the same, but similar enough to compare.
4. if you just want a little more bass then perhaps the hd518, 558, 598 lineup. mostly neutral sounding with more bass than the bass light headphones listed. more mellow and laid back though a little slower as well. good for long time easy listening and gaming due to these factors.
5. black and red you will likely only find in gaming headsets which are junk. black and silver/grey/tan are more common for professional grade/hifi headphones. there might be a few colorful options out there though...
6. the schiit plugs in to the wall since it is not a portable product and likely pulls more power than usb puts out. out of the two the schiit magni is by far the more powerful and quality product. the reason i said the e12 as an option is given its relatively high power output for the price which benefits certain headphones. there is a hum while charging i believe. some headphones may not need a strong amp or could be powered by a soundcard alone. honestly it depends on the choice in headphones and your preferences.
7. as i explained before dac = digital to analog converter. amp = amplifier. the dac works to convert the digital signal from your pc into an analog signal which is used by headphones. however on its own this signal is low level so needs to be amplified (increased in power) so that it can power the drivers in headphones. a soundcard is basically a dac+amp+software with a few other electronics. you need both a dac+amp to hear audio at all (onboard audio is this, soundcards are this, external dac+amp units are this... you're already using this combo) however i think you meant is it a good idea to have both an external dac and an external headphone amp and it really depends.
external amps can have more power output than soundcards. if you have high end or high demand headphones you can get more out of them than with a soundcard or low power amp. better quality on the dac end means less noise, distortion, quality generally. are soundcards worse than externals on quality (assuming power output isnt an issue) then no, some are good while others are decent. in short this:
soundcards: good if you want virtual surround (other than using razer's free software that is.. which doesnt need one), dont want to invest heavily into external products and have fairly easy to drive headphones.
external dac+amp: good if you do not mind stereo only audio of good quality (other than using razer virtual surround, or using a cheap soundcard to provide virtual surround.. for some reason it works a user responded back to me but i havent tested it myself). nice external volume knobs on the amp portion, high output on some models for power hungry cans. they do make combo dac+amp combos (e10k, audioengine d1, o2+odac, etc) as well or stacks like the schiit modi+magni. there is a product for most every situation or preference. some of it depends on what headphones you end up picking..
8. dt990 is a good choice if you like good treble and good bass output. the dt880 is a little more neutral sounding with less of a bass impact though still stronger than what your'e used to right now. the dt880 however isnt on sale like the dt990 is right now (dt990 pro 250 is what you should be looking at for value).
a good amp would be the schiit magni since its capable of bringing out the lower end on them. other amps/soundcards (creative z, fiio a3, etc) can power them but dont bring out the bass end as much as a decent amp will (low bass = more power to drive). if you want virtual surround i'd pair it up with a xonar dx on a desktop since that has a nice high quality dac onboard (same dac as on $230+ priced stx). as for on a laptop.. you could use the amplifier alone (direct to your laptop headphone jack) if your onboard is good. if its poor onboard then perhaps the xonar u3 (or u5/u7/omni if you can verify their virtual surround support).
9. audioengine d1 is a nice product for a good price though it has less output power than the magni. keep in mind its also a dac which means stereo only sound unless you use the razer virtual surround software. also, external dac do not have mic inputs on them. audio interfaces do, external soundcards do but not headphone dacs.
10. its possible of course. http/cdn.head-fi.org/3/31/3127ac42_LL1.jpeg
for example (console connectivity in the photo). due to double amping (mixamp has an amp in it) you might be able to get by with a lower priced amp though double amping also means more chance of distortion as well. the mixamp isnt a terrible product, though it fulfills the same function as an audio interface but with less options. if you absolutely want the features it has then go for it, but a soundcard may or may not have better virtual surround.
i would suggest listening (with headphones on and with your pc363d soundcard's virtual surround disabled) to youtube videos showcasing dolby headphone vs sbx/cmss3d vs razer surround and see which you like best. i think the mixamp uses dolby headphone and if that is the only selling feature you wanted (dont care about analog controls, etc) then the xonar u3 or other external soundcards do this for significantly cheaper price.