H6 is a little more refined than the M50W sub as it is a sealed sub vs a slotted port sub. But you are right, you should always get a bigger sub if possible. There is no such thing as overkill for a subwoofer, you can always turn the volume down.

You can leave it in the corner, the H10 is not a boomy sub and sealed sub is less sensitive to positioning.
The shipment may arrive in a few weeks indeed. You can already audition the speakers now if you wish. Don't worry about the source too much. The speaker itself is leaps and bounds above what you have at the moment.

Hivi h4 output mono rca. So u need mono to mono rca cable.

If ur sound card don't have rca input u will need Y spilter converter cable link 2 mono rca to 3.5mm aux

hf is treble (high frequency)
mf is mid or vocal (mid frequency)
lf is bass (low frequency)
hp is bass crossover (high pass)

i'm still struggling to calculate postage for each of the items to borneo region, cant put price in list, later i rugi gao gao :'(

they say m50w sounds like the mid is fuller and rich compare to sp2500, which only have highs and low, middle is very weak, plus the subwoofer and satelitte doesnt blend well. I dont know how would i like m50w.. now back miri,sarawak edi, dunno where to find demo set >< is it possible to buy H6 to pair with x3?

got! any home theater AV receiver got 5.1 DAC inside. from burr brown, cirrus logic, analog device to wolfson semua ada. usually digital conenction given is SPDIF coaxial, optical and HDMI. no usb input like stereo DAC in the market.

Top grade models use independent DAC for each channel, means 7.1 got 8 DAC working inside. u can look for pre-out to connect powered speaker like swan or hivi set.
depending on ur room size, big room might need 2x H10

Swans M200MKIII
https://www.youtube.com/watch?v=UClDjfxgCJo

Recommended!!!