Stereo preamp upgrade

Hello! I was hoping to get some advice from the last true audiophiles. Some time ago I purchased my first separates system after my college roommate got me into home audio. The system consists of a Rotel RC-1070 preamp, Rotel RB-1080 amp, Paradigm Studio Monitor 100 v2's, with Tara Labs and AQ power cords and IC's. Something isn't "right" with my system. I'm pretty sure it's my preamp.

I've had a great opportunity to hear a LOT of equipment, since my aforementioned roommate was a repair tech at a local hi-fi shop. He would bring really nice gear home constantly and we would audition his repair work, not to mention the equipment at the store. He had the same speakers as I have now so I know how they can sound.

The Rotel preamp is decent but the bass is not 'warm & soothing,' but has more of a raw feel. It seems to be tight and controlled, likely due to the amp, but it just doesn't seem to have that 'earthy' feel if that makes sense. The soundstage could be improved. It seems wide enough, given my crappy apartment acoustics, but the depth just isn't there. There is no 3rd dimension. Tonality is great. It's not dark or overly bright.

So, I'm looking for a recommendation for a new preamp. I only want a stereo preamp. I would love to have one with a optical input, but I suppose I could get a DAC instead (that's a whole 'nother subject), as I've begun to use a computer to play .flac's. I'm looking to spend around $500 and don't mind if it's used. I've considered the Adcom GFP-750 as I know it's a solid unit, but I don't have much experience in preamps.

What would you do in my position? Music comes first.
I'm not sure you're going to get a huge upgrade from the Rotel preamp, with a $500 used pre-amp. It's possible I guess, if you look at old enough C-J or Audio Research units.

If you had $1000, a C-J PF-R (SS), or a VTL TL-2.5 (tube), if you can find one used, would probably be a huge upgrade. There are also other used C-J tube pre-amps to consider.
The Parasound Halo P3 sells regularly on this site for around $500, it should present a different sonic character than the Rotel. I have not heard your pre-amp, but I use the Halo with an RB-1080 to push MA BX5s, and I'm fairly happy.
Your studio 100s are much nicer than the BX5s of course, they are on my "possible upgrade" list. In the Stereophile review of the 100s, John Atkinson states: "The impedance, however, drops below 4 ohms between 55Hz and 210Hz, with a minimum value of 3 ohms at 90Hz"..."A good 4 ohm-rated amplifier should be used with the speaker."
The RB-1080 is *not* a good 4 ohm amplifier. Something more along the lines of a McCormack DNA 1 might push your studios better, but these amps run about $700-$800 used. I'd suggest a new amp, not a new pre...
The Parasound is a solid recommendation. You won't find better than a Muse model 3 at that price point, I've seen them around $600. Be aware this is not a model 3 signature. The old Sumo Athena is surprisingly nice, probably around $300. The Adcom you mentioned is a good piece also, might be a bit detailed and edgy with the Rotel, But all of these will give you noticeably better performance than your RC-1070. I hope this helps,
What you want will have to be a future purchase, I'm afraid. The kind of sound you seem to want will come from some decent tube power amps. A lot of people start with a tubed pre. I found in my journey that it really wasn't the keys to the kingdom. If you want to go that tubed pre route, however, I heartily recommend a tubed pre by the AES division of Cary. The model is the AE-3, which sells used for less than $500 in certain iterations and rarely for more.
Unfortunately Upscale Audio is the last dealer Cary makes these pre amps for new. They put nice paint on it and filled it with options. This overstuffed version with stock tubes is $1200. That is not a lot for a good preamp but you will want to roll the tubes etc. It's really too bad that there is no base model to buy. Oh well!
One of the reasons I went with the Parasound is because of the remote. A remote is an absolute must for me in a pre-amp, as my listening sessions occur for hours on end while working behind a desk at home. This severely limited my options when hunting for an affordable pre-amp, otherwise I might have gone with another unit. If a remote is similarly important to you, make sure you check that box during your investigations.
Thanks for your honest advice. Speaking of a tube pre, I happen to have a Little Dot MKIV that I bought on a whim to tinker with that needs new tubes. It sounded fabulous at the time, but one of the driver tubes was shot so it didn't sound its best. I think I'll go tube hunting and see what I can come up with and give it a go. It's always fun to experiment and see what becomes of it.

The Rotel pre isn't a bad unit at all, but if it's going to cost over a grand to get into the next 'class,' I'll just save more money and explore my options.

Speaking of bass, I have an Electron Kinetics Eagle 2 that when it worked, had really nice control over the 100's. I can't recall hearing anything like it for the price. Maybe I'll send it off to get fixed.
Look for an older Audible Illusions, like a 2B or 2D or something. You should be able to get one in your price range, and musically, I don't think you can do much better.
If you can stretch your budget a bit a TAD Signature 150 would be a great choice. I recently acquired a N.E.W. P3 (made by Cary) for $525 and I'm very happy with it. With quality NOS tubes it equals the VTL 2.5 preamp that I had. AES also made my Cary has some nice preamps. An older Counterpoint SA-2000 is another alternative and well within your budget.
I suggest avoiding Audible Illusions. I had a Modulus 3 years back and it was hard on tubes. You're limited to specific tubes that can handle the abuse. I've read the rebuilt Dynaco PAS preamps using Van Alstine mods sound nice too for the money although I have not personally heard one. Whatever tube preamp you get you'll need to factor in additional cost or quality NOS tubes. They do make a difference. However, cost can add up quickly for good tubes. I tend to limit my preamp choices to preamps that use (6) or less tubes, preferably (4) to limit money needed for tubes.
Best wishes
Forgot to mention the Musical Fidelity A3CR... big value, should find one for about $500, This and the Muse I recommended earlier both have remote, the MF is single ended only, the Muse is single ended and balanced both. I recommend that you do some reading, If you are looking for ss at the $500 price range, these are tough to beat.
I second the CJ PFR recommendation. Unbelievable value.
Which tube does the Little Dot need? I may be able to give you some advice with my experience with the tube.
I think you can buy the AE-3 for under $500, maybe not the latest or fanciest models. Many AE-3s had remote control, so that isn't always a problem. Tube rolling is most important with it's amplification tubes which are 6SN7s. Fortunately these are abundant as NOS/OS and there are many bargains to be had outside the most sought after versions. Some models are tube rectified but they too are not overly expensive or rare, and plenty of people are satisfied with current production.
If you can get by without analog inputs, get a used Benchmark DAC-1, run its balanced outputs into the power amp and use the Benchmark's volume control. And you get a free headphone amp out of the deal. Experiment with the gain jumpers.
Thanks again for the rec's. This unit can use EF91, 92, & 95. I received some driver tubes today, a matched pair of Voshkod 6ZH1P-EV. I still want to get my hands on the Mullard M8100's, as I have a good idea of what they will sound like (nice!). I'm burning the Voshkod's in atm, and so far they sound pretty good. A little bright up top, but after burn-in they should calm down a bit. I'll experiment with the LDMKIV for a bit before I make a decision. If it works out, I may use it for music and the Rotel for movies. I have some power tubes coming as well.

I did want to run the idea of a DAC past you guys while I check up on your recommendations. What's your opinion on the Schiit Bifrost?
supposed to have a really good USB implementation, uses separate crystal oscillators for 44.1 and 48 kHz signals and their multiples, which avoids the creation of jitter in upconverting the 44.1 kHz signals, but reviews have stated that it sounds a bit more lean/bright/detailed than other more expensive offerings. I have not heard one, but it came down to the Bifrost or the Digital Link III, I went with the DL III. I use a Vlink with it, and I think the DL III sounds bright in my system. I am considering upgrading the speakers or the converter, might also toss in a Bifrost with a 30 day trial, just to see what happens...YMMV...