I know there has to a few Apollo users on here, and I've been looking at a lot of mic pres lately.  The Apollo has me a bit curious. I already have a UAD Octo card and lots of plugins, but if I understand correctly, the Apollo would allow me to record through a channel strip made up of UAD plugins and create my own flavor as I go, API, Neve, etc.  I guess it's the preamp side of things that has me intrigued a bit and considering replacing my existing setup with an Apollo.
 
My main questions are about the performance from a virtual instrument standpoint and the latency of playing virtual instruments.  Currently using RME FireFace 400 and it's working well for me, so I'd hate to lose anything in the performance there.  I'm thinking if the Apollo will do just about everything the RME does, plus add the DSP Pres, it might be worth selling a couple of items I have and going with the Apollo. Any thoughts?
Thanks

I imagine you'd be better off spending your money on a real preamp/channel strip than switching interfaces just so you can record w/ dsp going in.  I'll take real over virtual any time, just so you know where I'm coming from.
 
An ISA One, Warm or Warm Tonebeast cost less than an Apollo, will deliver real transformer goodness, not crap out if driven, give more gain for flexible micing techniques and sound great once in the box w/ a sense of 3D.  Rupert Neve Designs is my favorite preamp - they have a single channel model for about $700 I think.  I suppose it is the same as in my Portico II.
 
If you already have UAD for mixing, my thought would be to improve the front end rather than repeating.

Cool. That was kind of my way of thinking in the past. I've just been spending too much time reading about trying to find something better than my current setup and the options are a bit overwhelming. I think I'll continue on my current path with the incoming ISA Two for clean, then sell my 4-710d and get a single channel workhorse for the color preamp.  I might even be able to keep things clean going in and use plugins for all of my color in the mix too, so I might even be able to just live without that 4-channel monster.

Genghis,
 
I recently traded in my RMEFF800 for an Apollo Twin that I use at the office for voice-overs, and, an Apollo Quad for home studio.   The Unison feature you are inquiring about is very cool.   I find I spend a lot less time mixing and tweaking when I have recorded through the UAD Pre-amps via unison.   I have the NEVE1073, the UAD 610B and the API Vision Channel Strip (all Unison capable)  
 
Personally, I would highly recommend this route over an external pre since you are already invested in UA.  Some new capabilities with Console 2 allow you to combine device processing resources (currently only Thunderbolt but Fireware is coming soon)   Check out some of the Channel Strip/Pre-amp videos on UA's site.

I am using an Apollo QUAD as my primary audio interface. It works flawlessly with SONAR Platinum. Been I longtime UAD user (have most of the plug-ins) and being able to use them in realtime (recording/monitoring) is simply a dream come true. Next best thing to using the actual hardware. The Unison technology is an added feature that allows UA to model mic pre's as accurately as possible using a software/hardware hybrid approach. So plug-ins not only sound, but behave like the hardware. The new version 2.0 Apollo Console is only available for Apple TB computers, but UA has announced that a FW version will be released in the Fall. This recent video gives you the basic Apollo concepts using the included base UAD plug-ins. Of course you can substitute and use any UAD plug-ins that you have.
I really like using the updated LA2A, Pultec, 1176 & Fairchild Collections along with my EMT 140, 250, 224 & RMX16.
Then add in some mic pre flavor (1073, API, 610's, etc) via Unison, when needed.
 
https://www.youtube.com/watch?v=-tKMgnkPxXY
 
Cheers,
 
Billy Buck

Man... you guys make it sound really tempting.  Still curious about how it performs with the software synths.  Will it be comparable to the RME in round-trip latency?

Genghis,
 
In general, there is no discernible latency when using Unison to record/print.   I leave my system at 1024 samples all the time now (even recording through the Apollo with effects) and cannot hear any delay.   Typically will use a pre-amp and usually some light compression for everything.  May use a guitar amp or other guitar effects for certain styles, and that also works without latency.   Do not use Input Monitoring for this process.       If you are into guitar, check out Pete Thorn's UAD videos on YouTube.  Here is the 1st one:
 
https://www.youtube.com/watch?v=G3_HujiPlkw
 
Of course, when you introduce certain types of plugs from any manufacturer into a Sonar track or Bus, you will introduce latency.   The UAD Precision Multiband introduces very high latency for example) I typically print everything prior to adding any high latency plugs to the project file.
 
Regards

I understand what you are saying as far as using Unison to print UAD effects.  My concern is how it performs with buffers set to 128 or so for using software synths.  It seems to be a popular interface for people who record instruments and voice, but I'm just unsure if it will provide the low-latency when I run virtual instruments that I get from my RME.  I do kind of a mix between virtual synths and recording of voice and instruments.

It will depend on your system to some extent.   Since switching to the Apollo, I honestly don't even think about changing buffers or their settings, just leave it set at 1024 all the time, even when recording.   My biggest project as far as resources was a cover of Mama by Genesis. 
 
http://forum.cakewalk.com/Mama-Genesis-Cover-featuring-Alkie-on-vocals-Updated-Version-m3095564.aspx
 
This project had 5 instances of various Arturia Synths, 1 UVI synth, Trillian, 1 Superior Drummer, 1 EZDrummer 2 Electronic Kit,  none of them were frozen or bounced and the guitar parts were recorded last without any problems though one of the UAD Guitar Amp sims.   I count 8 virtual instruments which is a lot for me...
 
I also should note that this project was done with Thunderbolt connection to my MacBook Pro so Firewire may not have the same result.   The Apollo was also at 98% DSP utilization for this song.  
 
I see you have a Jim Roseberry system, he could probably shed some light on what kind of performance you would see on Windows 7, Firewire with an Apollo.

Regards

AT
I imagine you'd be better off spending your money on a real preamp/channel strip than switching interfaces just so you can record w/ dsp going in.  I'll take real over virtual any time, just so you know where I'm coming from.
 
An ISA One, Warm or Warm Tonebeast cost less than an Apollo, will deliver real transformer goodness, not crap out if driven, give more gain for flexible micing techniques and sound great once in the box w/ a sense of 3D.  Rupert Neve Designs is my favorite preamp - they have a single channel model for about $700 I think.  I suppose it is the same as in my Portico II.
 
If you already have UAD for mixing, my thought would be to improve the front end rather than repeating.

Absolutely perfect advice!
 
OP has a great audio interface... and top-notch plugins.  
Round-trip latency of the Apollo would be higher... and thus a step backward.
Fidelity of Apollo is very good... 
 
If you've got a great audio interface, it makes sense to invest in the "front end" (mics/preamps).
Capturing the best possible source will have tremendous impact on final results.