I am asked to do a project for one of my friends.A data Acqusion system or better to say something like a DSO.
There are 2 fast ADC chips that i found available here : HI1175 , TDA8703 .
The TDA one looks too much old and discontinued and is only available in DIP for about $10.But the HI1175 is available in SMD (24Lead SOIC) for $5.I prefer to Use SMD chips for this project.
There are some ready made designs available on the net here are the ones I found :

TDA based :
DSOA Mk3
MiniDS
1175 Based :
Simple USB one

The above designs are somehow old (except the last one).I would be appreciated to have your opinions about these things :

Input stage :
1- http://www.edn.com/archives/1996/090296/18di3.htm
2- http://www.eix.co.uk/Ethernet/USB/image016
3- http://www.8052.com/users/farshidjh/atgain.GIF
4- http://alternatezone.com/electroni...k3anal.gif

Number 3 was the one i thought about sometimes ago but I've read that 74HC4066's show a series resistance about 90 ohms.
What are your suggestions , which of these are better ? I think The last one is the best. Is it possible to omit the second and third Op-Amp and do everything in the first stage ?

Digital and storage Stage :
Personally I would like to have a USB2 connection and take all of the 20 Mega Samples/s transfered to PC's memory (160mbit/s < 480mbits,USB2's maximum).For this reason i thinking about using a CPLD or something alike for the easiness but I am new to the Programmable Logic.This way I'll have to a use a little buffer i think.
Since I didn't seen any USB2 controller available locally I think I'll have to omit the idea.
What are your Ideas about Buffer and controller section.
I don't know how exactly the trigger signal and trigger detect works, I'm reading more on this , I'll be appreciated if you could give me any Info.

Building a DSO was my friends idea .I knew that such a thing is supposed to be built by a very good analog designer but since he insists in such a project I want to do my best to make it better for him.The whole thing would run on a double sided PCB with separated Ground planes and analog/vcc supplies.

Thanks in Advance,
Farshid