Fireface400/UC - Which one for more inputs/outputs

Hi there

I'm looking to purchase an additional interface to boost my analogue input/output capacity.

I already have an RME MultifaceII (PCIe) and was thinking of getting an RME Fireface400 or RME FirefaceUC. I would be able to hook this up to my MultifaceII as a stand-alone convertor expanding my analogue inputs/outputs via adat.

Due to not requiring to use the Fireface400/UC's firewire/USB cable in the above setup, whichever of the two I buy is of no consequence to my main DAW setup. However, the purchase of a Fireface400/UC would enable me the flexibility of taking it out of my rack for location recordings with a laptop when/if needed.

Incidentally, my laptop (purchased without audio in mind) is a fairly cheap Acer which has an 'AMD 64 Athlon x2' CPU. However, I upgraded it to 4GB RAM and 2 x 500GB 5400RPM 8MB Cache Sata Hard Drives. Wouldn't this system, at least, manage modest track count recordings (5-10 tracks) which could be transported to my main DAW later?

I should point out at this point that my laptop has XP 32 bit and my DAW has Win 7 64 with Sonar X1 64. Are files interchangable between 32 bit and 64 bit Operating systems and different bit Sonar versions?

The reason I'm asking for opinions about my laptop's capacity is that I'm unsure I would be using a Fireface400/UC for this purpose very often. Therefore, my potential location recording needs couldn't really justify a major high spec laptop purchase to accommodate.  

My only decision is really Firewire or USB 2.0? I believe Firewire has the edge? Is this correct?

I have both Firewire and USB 2.0 ports in abundance, on my main DAW with my Firewire Ports being Texas Instruments Chipset. This would enable me to handle either a Fireface400 or FirefaceUC should I wish to have a MultifaceII and Fireface operating as two soundcards in my main DAW - 16 x analogues, 16 x adat and 4 x s/pdif. Note: that this setup is different from my main objective stated at the beginning of the post.

My laptop has an abundance of USB 2.0 ports but has only one 4-pin Firewire port which is OHCI chipset. Am I correct in my understanding that hooking up a Fireface400 to this may be a gamble in that may possibly not work?

In contrast to the Fireface400 (firewire), would I be at a latency/data transfer disadvantage going the FirefaceUC (USB 2.0) route if using the unit as a sound card?

Although my main envisaged use of a Fireface is for analogue input/output extension via adat, I thought it best to get an informed view of the pros and cons of each protocol as they relate to their performance as interfaces in their own right. Any input would be greatly appreciated.


Regards

Stewart