In terms of audio quality and scalability, does anyone has any idea on which one is more preferable?

Thx thx thx..

When people talk bout difference in sound quality it is hard to answer because very few of us have professional studios.. If you got thousands of bucks worth of Mics,$1500 monitors, and sound proofed rooms and the whole bit,then I whatever teeny difference threr possibly ma be in sound quality could matter.. I am assuming you are talkig about the DigIoo2 Rack, since the regular one is a control surface as well as an interface.. If you are doing lots of MIKing, ten for the same price of the Digi )2 Rack you may consider the the MOTU 806...
Anyways, I am a MOTU fan, its literl translation is Phat (in Hindi)
While Digi, in Aborgenee means blows (I dont lnow about that one acutally, but it is possible..)

Thx for your reply Saurabh, in fact, i'm going to upgrade my recording kits, i'm still using DP2.51 with Audiomedia III PCI cards for years, and considering going to either ProTools or stick with MOTU, and upgrade my DP and adding a 828mkII or 2408mk3 (possibly with a new G5 dual-2G as well~).

But i know very little about ProTools, and to be more specific, i want to know whether there's anything the ProTools is capable of but is impossible/nearly impossible with the MOTU gears aforementioned.

Both programs are capable of the same stuff. Although ProTools Le has soem Limitiations on number of Audio tracks, but I doubt that is a problem for most.. i have seen some Protools HD users use DP4 and other prorgrams besides Protools as thier main DAW, so it is a matter of preference.. I tend to find the prices of Motu hardware and software much more to my liking. I am not saying its cheap, but just more resonable... The 2408mk3 is another greatchoice, but it has no mic pre amps, so you'll need a mixer to use some mics.. Also, the 2408mk3 is PCI based, so not useful when on the go... Unless you get the 896, that has 8 beautiful mic preamps (Neutrik connctions), that have indiviudal Phantom power, and gain controls, You will need a small mixer to Mic more than 2 instruments at once.. If 2 MIcs is all u need , then you have no problems, and the 828mk2 would be my choice..So. to boil it down, you need to ask yoursself, how many Mcs will I be recording with at once, and do I need to take this system on the road..
BTW, Are ou really going to use the 24bit 96khz to record your music? If not u can get great tdeals on the old models that are 24 bit 48khz.. i am talking 50-70%off!!!! You can buy a couple of great mics with the money you save, or whatever else you wanted..Come to think of it, The new G5's have 24bit , 192Khz capable sound cards built in. You get an older Motu, then use the MOTUs optical outputs into the G5's opitcial input, and record at 192 Khz if you want, and save hell of a lot of cash!!!
Good Luck, I know its getting confusing, the more I write, the more idea's i come up with..
I guess I would buy an older Motu audio interface, saving half the money i would spend on a new one. Then use the optical output into a new G5's optical input if iwas ever going to record above 48khz (which I doubt i will for at least a few more years)..

Thx for your thoughtful opinion. Yes, you're right, the mobility of the kit is surely one of the critical factor to be considered. In fact, the new gears will only reside on my rack in the recording studio, so i guess most probably i'll get a 2408mk3, and leave room for HD192s on the PCI-424 if needed.

828mkII is nice, too if i have a handful of spare money in the future, i'll get a powerbook-15 with that.

another issue between PT LE and DP is that DP 3 and above can do surround mixing and the only ProTools systems that can do surround are the TDM and HD. Its possible to run a multiple channel mix in PT LE but the panners in the mixer are still all just 2-channel, stereo. This means you can pan from L to R or Ls to Rs, but you can't pan from L to Ls (front to back or anywhere in between).

In DP 3 and I assume 4, you have panners that look like a joystick and allow you to pan a mono or stereo track anywhere for true surround panning (including automation). Also, DP has the built in sends and plug-ins necessary to create a real .1 LFE (subwoofer) channel. To do that in PT LE, you'd have to set up your own send/aux and put a low pass filter on it manually.

I'm very much into surround (and with the new Alesis 5.1 speaker system, it isn't that expensive to get into it) so even though I essentially like the PT interface better, DP is the only way for me to go. The cost of even a used TDM system with enough DSP power to do surround with plugins is still over $5,000.