This may probably not make any sense but I am trying to see I can get the stability of RME and the I/O in the scarlett 18i20 into one setup.
 
I am looking for an audio interface with more I/O than the basic Scarlett 2i2 that I currently use.I'm working this out from a budget perspective. I can get an UCX but I get only 2 mic pres with it. If I connect the Scarlett 18i20 to the Babyface, I get 8 additional mic pres for almost the same cost  (in my country) as the UCX. I like the  scarlett 18i20 for its i/o, but also want the  driver stability and latency provided by RME.
 
So the questions are :
Is it technically possible to connect these 2 interfaces to the computer and be able to use the Babyface as the primary interface for playback, or is this whole setup just inviting technical issues (in general and esp with Sonar).
 
Can I connect the Scarlett's ADAT out to the Babyface's ADAT in and be able to leverage the mic pres  on the Scarlett?
I am assuming I can connect the headphone out from babyface to the line in the scarlett and leverage the 2 additional headphone outs on the scarlett? Does this make sense? Im suspecting headphone out levels would'nt match the line input levels.
 
Would it be a simpler and to the point solution to just get another mic preamp box and use it with babyface , rather than a complete second audio interface? I'm thinking I cannot  anyway leverage all the line ins and outs and the mic pres on the scarlett 18i20 given that the babyface has only 1 ADAT in and that can take only 8 channels (or less based on sample rate).
 
 
 
 
 
 

You're asking for simpler. And you are budgeting.  I get that you want to increase your inputs, but I don't see any need stated by your for 20 outputs.  I suggest you consider getting the 2nd Gen 18i8 (I have two of these).  You'll get your 18 inputs with the one unit.  (Well, to be clear, you need a second device with ADAT to provide 8 of those 18).   You have the expandability to have 18 inputs, put it that way.
 
The 2nd Gen 18i8 has great drivers, latency is gone.  Works terrific with Sonar.  Solidly built.
 
Goes for roughly 1/2 to 1/3 of the price of the RME.  So, sure, you can buy an RME.  But if then you're looking to buy even another unit to get up to 18 inputs, why not just get the one that has 18 inputs?  It works fantastic as is.
 
The extra outputs (20) seems pretty over the top for your home recording needs unless you have wider plans.

You should be able to plug ADAT to ADAT and get 8 additional audio lines into the Babyface.  That is the point of ADAT, tho some times there are sync problems.
 
You won't be able to use a single headphone output to provide 2 different headphone mixes.  The RME headphone out can go to an input on the Focusrite and that single stereo signal can be output to both of the Focusrite's headphones if loud enough, that depends.  You will need to the proper connections if the RME headphone is 1/8 inch.  Your better bet would be using the ADAT out (if available on the RME) to the Scarlett ADAD input (if it is available - some units save money by making the ADAT one way, not both the input and output) and routing 4 channels it to the 2 separate headphone outs that way (giving you 3 headphone mixes - RME and 2 Scarletts).  

AT
You should be able to plug ADAT to ADAT and get 8 additional audio lines into the Babyface.  That is the point of ADAT, tho some times there are sync problems.
 
You won't be able to use a single headphone output to provide 2 different headphone mixes.  The RME headphone out can go to an input on the Focusrite and that single stereo signal can be output to both of the Focusrite's headphones if loud enough, that depends.  You will need to the proper connections if the RME headphone is 1/8 inch.  Your better bet would be using the ADAT out (if available on the RME) to the Scarlett ADAD input (if it is available - some units save money by making the ADAT one way, not both the input and output) and routing 4 channels it to the 2 separate headphone outs that way (giving you 3 headphone mixes - RME and 2 Scarletts).  

Thanks for the info. Will I need to plug the scarlett to the PC at all or will it run standalone ?

lawajava
You're asking for simpler. And you are budgeting.  I get that you want to increase your inputs, but I don't see any need stated by your for 20 outputs.  I suggest you consider getting the 2nd Gen 18i8 (I have two of these).  You'll get your 18 inputs with the one unit.  (Well, to be clear, you need a second device with ADAT to provide 8 of those 18).   You have the expandability to have 18 inputs, put it that way.
 
The 2nd Gen 18i8 has great drivers, latency is gone.  Works terrific with Sonar.  Solidly built.
 
Goes for roughly 1/2 to 1/3 of the price of the RME.  So, sure, you can buy an RME.  But if then you're looking to buy even another unit to get up to 18 inputs, why not just get the one that has 18 inputs?  It works fantastic as is.
 
The extra outputs (20) seems pretty over the top for your home recording needs unless you have wider plans.

Yes, im expanding , I dont need 20 inputs and outputs right aaway, may be 6 , but I want to just get future proofed so I dont have to change the interface in another year and a half or 2.
 
The reason Im skeptical to use scarlet as the primary interface is my bad experience with the 2i2 first gen. But you say second gen is more reliable !

Personally I went down the road of adding a Focusrite Octopre to my RME UFX to get more inputs (line ones in my case rather than mic pres). The connection between the two is an ADAT cable and word clock. There is no direct connection between computer and Octopre and RME's Totalmix handles routings and levels.
 
You might find this useful, it's about the UFX but the principles are the same whatever the interface is. https://www.forum.rme-aud...viewtopic.php?id=18121