I am looking at upgrading from my Sapphire 8i6 to an interface that will allow me to record more that two tracks at one time. So as far as an upgrade - what is a good introductory interface that can send 6 or 8 channels to my DAW? In some of the descriptions I read they talk about plenty of outputs, but they don't clearly address this question (to me anyway). Is USB/Firewire always restricted to stereo /two channel recording to a laptop no matter how many inputs the interface has??  thanks

http://www.sweetwater.com...annel_Preamps/low2high

I have a Focusrite Saffire Pro 24 Firewire.
 
has 16 in's 8 outs.  I have it on a dedicated Firewire card running at Firewire 400.
 
I have no problem recording 4 of my hardware synths stereo (8 input channels to accommodate L/R).
 
my CPU is 3.8ghz and I have 32gb ram and SSD drives in my desktop DAW rig.
 
if you have a laptop with a slow hard drive, not much ram and record at a high rate you may introduce a lot of latency when recording.
 
depends on what your computer specs are as it all has to work together.

Since you're already accustomed to Focusrite products, it would make sense to just go with one of the 8i6's multi-channel siblings. They're inexpensive and pretty decent interfaces. I currently use a Saffire Pro 40, which was half the price of the MOTU 828Mk2 it replaced but provides nearly identical functionality.

Is USB/Firewire always restricted to stereo /two channel recording to a laptop no matter how many inputs the interface has??  thanks
 
This is only true of a few Mixers like Mackie and Behringer that are 12 or 16 channel mixers but only have a 2 Channel USB interface. 
Go to Sweetwater, Musicians Friend or any on line music store and look up Audio interfaces, there are dozens and dozens of multi channel interfaces. 
 
I have the old Tascam us1641 which is now called the us1800 and then the brand new model the US16x08 as example of 16 channels for only $300. Then there's the Focusrite Scarlett 18i8 which is around $350. Presonus is also popular. 

Hey hold the phone !!   A search for Sapphire 8i6 takes me to info about the Scarlett 8i6, Sapphires never had numbers like that. So if you have the Scarlett 8i6 you already own a 8 input interface...Are you just not setting it up right? 

you should adjust your setting and inputs in sonar. i use RME and UAD for recording and both have multiple inputs and outputs. I record concerts with 16 mic in to my Daw and it's working just great.
 
so you have to adjust sonar input to have them all recording. or whatever number of mics do you have. 

As pointed out above, the saffire unit has 2 mic preamps, 2 separate line inputs and digital spdif in/outs.  If you have a mixer or outboard preamps you are good to go for two more channels.  If you get something like the Tascam uh-7000 you can use its superior preamps and conversion over the spdif digital in - and out for montitoring.  That gives you 6 inputs at once.  The uh7000 is $400.
 
That would be a cheap way to improve inputs and quality.  Otherwise, how much are you thinking of spending?  I saw a bigger Focusrite for $500, tho I don't think you can aggregate it w/ your unit.  Lynx has a new 4 x 4 pcie unit coming out.  If it is priced like the old unit it will be $1000+, but it includes 2 digital in/outs so you could use the saffire.  Or just buy Burl. 
 
A price range would help.

So one more question about this issue of number of channels / tracks that can be recorded - about a USB Mixer. Take for example the Mackie ProFX12 Compact Mixer with Effects and USB - I have written to them to find out, perhaps someone knows if this usb carries just the main stereo out, or can each pre-amp channel be recorded... thanks ! 

 
The Mackie is a only a stereo interface @ $299 that's what you'll get. The 8 channel to DAW version is $650.  http://www.mackie.com/products/dlseries/
All those budget USB mixers drivers are not very good for Sonar.  They are not intended to be used as an interface. It's for stereo board mixes and playback. 
  
You are not really engaging in this thread very well ( 3 weeks to reply to your own questions) so I'll be brief. I am more then willing to sort this mystery out for you if you could just get back in a timely manner please.
First I think you own the interface shown below. If this is correct you already have 2 XLR inputs, 2 TRS inputs and SPDIF for a total of 6. If it is not, could you supply a link to the product page please.