first of all, thank you for all the experience expert, who gave me a hand at free of charge.

Now, my wallet is in ICU.
back to the topic.
final decision 2080....... why?
2075($2380): disadvantage ~ only 6L of filter material space, so it must be out.
2076($3500): disadvantage ~ only 6.6L of filter material space, so it must be out.
2078($3950): 8.6L of filter material space and can be consider. however, it got the computer to make the water wave. but, i don't need it anyway. the more function it got, the sooner it will break.
2080($3950): 12L of filter material space. it have more space for the filter materials so I pick this.

(if my shelf is tall enough to put it).
for 2080, it come with 5L dazs filter material. can be deduct about $300 if i don't take it. Should I change it to MA M SIZE (MA is around $660/10L)? which brand is better? There are three baskets for the filter materials, should I put all in the same filtering material?in case if the flow rate is too strong, there is a flow rate control on the top of the canister to make it weaker.