it seems that you are already pretty happy with how your speakers sound which to me makes it seem like a waste to get new speakers. generally unless you're not happy with how your current speakers sound i wouldnt suggest it. that and the microlabs do not seem like much of an upgrade over what you have now. also realize that having speakers with their own amp/inputs not a receiver also severely limits you on the types and number of sources you can use.
while you of course dont have to follow my opinion, since you do not want to deal with a soundcard and since you use a tv for both sources you might want to think about upgrading to a newer receiver which supports hdmi and keeping your old speakers. if you play your cards right you could upgrade your speakers at a later date (to something which actually would be an upgrade) to use with this new receiver if you ever felt the need for an upgrade.
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perhaps a little on what i use myself..
i originally bought and used a logitech 5.1 setup (x530 which is better than the current z506) along with a soundcard. about 4 years ago or so i upgraded to a receiver and speaker system after not being happy with the other options given to me. i may have spent more but it was well worthwhile and i dont think i could ever be happy with pc speakers now that i've heard the difference. i use an hdmi capable receiver to swap between a pc, ps3, ps2 (running it on component cables), laptop and other sources and it works great. 5.1 support on pc is uncompressed (PCM), same on ps3. while it seems like pc/ps3 have slightly different sound, both i would say sound good to me.
i currently use a pioneer vsx-30 receiver paired with the 5.0 klipsch quintet set and a sw450 klipsch subwoofer. photos in signature or here
http
/goo.gl/zcmFbN which is hooked up to my gaming pc and all my components.
in the other room we use a sony strdh540 paired up with some sony fs-f500p floorstanders. while the receiver is not as nice for sure it does offer some pretty good output power for the extremely low price we paid for it. overall a good discount buy i'd have to say.
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optical vs 3.5mm:
optical is pure digital.
3.5mm is analog.
digital generally is less affected by electrical noise, and optical the least of all digital cables. however, generally unless you have something generating some pretty mean interference you arent going to notice it on 3.5mm.
it should be noted that 3.5mm since its an analog signal and already processed and converted to analog from its digital origin is uncompressed sound. if you ignore the possibility of electrical noise interference completely, 3.5mm can technically be superior. however also worth noting that almost no decent hifi sets use 3.5mm input for 5.1 and generally your selection of speakers with 3.5mm is pretty poor. it should also be mentioned that 3.5mm is amped which means to use powerful speakers with it you would need to double-amp which means a loss of clarity. basically: while they can be compared they are both used in two different scenarios so are more like apples vs oranges. both fruits, but different.
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other than that, its only a connection type. what matters more is the hardware driving the connection. a good soundcard (dac+amp) driving 3.5mm makes a big difference and likewise having propper support for 5.1 over optical and a decent sound chip can mean the difference between optical working for you and not.
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to recap: i'm thinking getting a new receiver may fit your needs best.
you're free to make your own choices of course.