Things that affect sound are, in order of degree of affect are:

1) Speakers
2) Room (Some would argue that the room can have a greater effect than the speaker, and for very low frequencies, this is very possible.)
3) Amps
4) Source
5) Preamp/Processor

So, if all else stays the same, a preamp can affect the sound. The question is: does it do so in an audible fashion? Obviously, if the preamp is a poor one, the answer can be "Yes". Let's consider just good pre/pros, then.

While digital processing has removed much of the possibility for introducing analog noise and non-linearities, it can cause problems of it's own. One has to consider roundoff error in the processing algorithms, whether the analog signal sampled was properly band-limited (foldover distortion will result otherwise), and sampling jitter in A/D, and, more problematically, D/A. The final D/A stage also has a filter to remove resampling artifacts.

All of these can contribute distortion: DACs, particularly in consumer gear, are not perfect, and their clocks can jitter all over the place.

Assuming the quality of the digital processing is the same across all manufacturers, the final analog stages tend to be most crucial. Upsampling, particularly, can have an effect here, because it determines the quality and steepness requirements of the output filter, sometimes a combination of an analog and digital filter. Google for "noise shaping". The bottom line, is that one can use a less severe output filter with increased upsampling rates (and that translates into less phase distortion at higher frequencies). Of course, if increased resampling can make an output filter (integrater, really), work better, there may be the tendency to try to use an inferior output filter to get the "same" quality as one would get with a better filter and less upsampling. Increased upsampling also requires tighter jitter tolerances.

All of these are tradeoffs. Do they affect the sound in a manner that is noticible? Perhaps: jitter distortion is particularly nasty (witness the harshness of early 1980s CD players with poor clocks, no buffering, and hard output filters).

Of course, it should be difficult to notice differences between any decent pre/pro, suggesting that features and price be the primary factors determining what one should purchase (support and appearance being others). I suspect few could tell in a double-blind test. But, there is no guarantee that a $1100 pre/pro isn't just repackaged junk at a high price.

Problems start when a reviewer finds a pre/pro "bright". Does that mean lousy output filters, poor DSP algorithms, or a very slight perception that high frequencies are emphasized? In other words, just "how bright" is it? If the pre/pro is otherwise recommended, probably not a lot.

Now, with regard to Outlaw, their M200 monoblocks have a documented tendency to roll off the high end above 10 KHz. Could Outlaw have tried to compensate by making their pre/pro intentionally bright, if ever so slightly? Some manufacturers are big proponents of "component synergy". I suspect this is a marketting ploy to sell you everything from source to pre/pro to amps to speakers, and it might be possible that individual components are made intentionally less than ideal to pull this off.

But, such chicanary can be found by measurements, and AFAIK, no such emphasis is seen with the 990.

I own a 990, and am extremely pleased with it, even though I'm just using it in a 2.0+LFE configuration for now, replacing a 20 year old analog preamp that cost $2500 at the time (and I would admit that half of that was for the "B&O 5500 look"). Balanced outputs, bypass mode, number of inputs, component and DVI switching, and price were the determining factors for me.

I would consider the Rotel a decent pre/pro, probably on a par with the 990, but with all the "overhead" of a retail sales network, and the markup that entails. Bottom line: the 990 is better value for at least the same performance.