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.