There appear to be two different conversations going on here.  Folks, he's got a MOTU Ultralite and a Blue Robbie mic pre.
 
I'm not a guitar player, but it sounds to me like he's asking about getting a better guitar tone into his DAW recordings....

Actually, the DI's I am using have very clean db pads (on the Pro48) and volume level controls (on the MXR 80).
So the incoming signal that gets recorded is already at a good level and very clean with no added hiss or noise.  I have each individual incoming level calibrated to average between -18db and -12db which is where I like to record so that the final mix is around -6db.  I always thought that the preamps were simply to smooth and possibly color your incoming signal...I never thought of using them in regards to helping increase the signal level.  However, that is only the case for my instruments...bass, guitar, etc.  I do use my Blue Robbie preamp to boost the level of my vocals but I don't run my instruments through it.....too much plugging and unplugging between vocals, keyboards, bass, electric guitar, acoustic guitar, etc. 

Hi Mojo,
are you recordimg/splitting with your Di Box two signals of  the guitar´s, bass aso?
If not, I recommend to record the Di signal for transients, emulations aso and the miced signal
(eventually a new mic?)for "room., warmth aso."
But I guess you already are doing that,or?
 
 The preamps and Di you are using are imo  very good. 

Hey Pragi,
 
No...I haven't split the signal from the DI to the DAW and mic'd amp.  I'm only recording the straight DI'd signal.  I use Amplitube for all of the amp/cab/room simulations once inside Sonar.  Thanks, I've been VERY happy with those DI's as well.  Extremely clean.

"Radial Pro 48 DI"
"MXR 80 DI +"
 
 
Both of those devices have pre amps built inside them.
 
best regards,
mike

You can use what ever you want, as long as you get your desired sound. Its that simple./ One is not better than the other. You use what is needed, period!
 
CJ

mike_mccue
"Radial Pro 48 DI"
"MXR 80 DI +"
  
Both of those devices have pre amps built inside them.
 

Thanks Mike.  I knew that the MXR had a built in preamp, but I wasn't aware that the Pro 48 had one as well.  That would explain why I don't have any problem with the line levels not being sufficient.  So, it looks like I have decent quality preamps for line instruments as well as vocals.  Pro 48 for guitar...MXR 80 for bass...Blue Robbie for vocals.  I was not at all happy with the Alesis MicTube Duo's that I was using.  WAYYYY too muddy even after I upgraded the tubes.  Since I no longer need them, I guess they're headed for ebay. 

I'm VERY happy with my Saffire, having owned sub-par preamp/interfaces from M-Audio and Roland in the past. I can't imagine not having external gain staging capability, so I can manage signal levels to always be in the sweet spot and decouple from sound production. It is certainly necessary if you want to mike an amp. Even my Rhodes Stage piano gets a tube preamp and simple compression (ART and RNC respectively) before hitting the Saffire, as I can optimize the sound that goes in without using dynamic range. 

a preamp is merely, well, an amplifier that brings up a signal to a level the next piece of equipment can use effectively.  Reciever amplifiers for old home studios had preamps for turntables (and eq), just as mics need preamplifiers to raise their level where line level equipment can use it, or a DI raises the small signal produced by guitar pickups to line level.  Most mic preamps have a di in it too.
 
The more experienced you become at recording, the more you hear the very subtle differences preamps especially produce.  The easiest thing to find is the available gain.  An external high-end preamp will have 10 - 15 dB of gain more than your garden variety interface preamp.  If you are close miking or miking loud sources, your interface preamp will work very well, thank you.  For softer voices etc. that extra gain makes a difference.  And then you learn to use distance when miking, backing the mic off of the source if you have a half decent room, which brings out the air in a source, so it isn't a flat, 2 dimensional sound but blooms and breathes.  Then you notice w/ good (read expensive) analog you start hearing the transfomers work and other high quality goodies stuffed inside these expensive boxes.  Transfomers tend to round off the sound and work good w/ the "sharpness" of digital recording.  And all those other good bits start reminding you of the sound of your favorite recordings which, probably, include those same bits.
 
And this is all at the edge of perception and is the last 10% or less of the sound, but is real if not exactly quantifiable.  So you get into the placebo end of things.  I hear, therefore I think.  Maybe someone else doesnt hear it, but the engineer works hard to get the sound - even if he is the only one.  And because he (or she) is working w/ good stuff, they don't allow themselves to compromise the sound because it sure ain't the equipment at fault.
 
So you don't have to go out and buy a $3000 channel strip to get a good sound, but if you keep at recording you sure would like one.  There is probably very little difference between a decent $4-500 preamp and a $1500 one, but you'll find engineers - good engineers, who won't work w/ the former.  Because they don't have to.
 
Don't let your interface preamps stop you from making good - even great recordings.  It is mostly the song, anyway.  But if you keep at it you'll probably discover an expensive habit.
 
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