Great subject, i'll chime in...
First, what sound are you after?
"I'm using a mono synth, guitar with a bunch of pedals, and some drum samples in ableton.
I have a bit to haul around, so I'm trying to minimize the amount of equipment that I have. Which leads me to...."
"Issue One: Guitar DI vs Amp
I have a fender bandmaster reverb that sounds amazing. It isn't feasible to carry around the amp+cab, pedals, keyboards, etc. This has led me to going DI, but alas, it sounds bad. I've considered a small 1x12 mic'ed, but then the fullness of the guitar starts to take everything over. Is there any way to get a decent sound running DI? Can I somehow run a dummy load from my amp head, then send the line out signal to my interface? What about running the output of ableton to my tube amp?"
I LOVE AMPS, I'm lucky enough to have friend who builds world class amps, mostly Dumble style but with many special tweaks.. so I love amps.. BUT i have found the a cheap V-stack tweedy is actually good enough for much of my playing... the trick is to always use a bit of reverb and or echo to compensate for the drieness if a line approach.. much the same goes for closed miked amp, it need a touch of room sound to sound realistic. Also the new PODs are not bad and stuff like ElevenRack, GuitarFX and Kempler can sound absolutely amazing if you turn of noise gates and compression.
You can dummy load the amp with several types of attenuators like THD, Weber Mass and that type of stuff. To me the loss of the live feel of a speaker makes it sound a lot like a amp sim...
"Issue Two: Analog Synth and Guitars
I use my mono synth mainly for bass sounds. I would like to get a juno at some point, but for now, I'm sampling the synth and doing poly that way. I have a hard time figuring out how extreme the eq'ing should be though. Does anyone have suggested reading material for mixing guitar and analog synths? "
"Issue Three: Mixing electronic sounds and acoustic sounds
Is anyone else mixing acoustic sounds and electronic sounds? I'm having issues with the electronics sounding a bit sterile. I've even tried synthesizing my own sounds to match the guitar, but it seems to be a constant problem."
Maybe these two questions are the same, how the not get the electronic and synth sounds collide with the guitar frequencies. I think that a good approach is to tailor the syntsound FIRST so that the are complementing the guitar. As an example i made a "patch" on my octa track that live samples my guitar and change pitch so make it into a bass sound, on that I use a LP filter to take away a lot of the frequencies that compete with guitar. As for electronic sound i construct the from live sampled guitar I gives them a more organic fee. Another feasable way is to keep them sounding as electronic as possible to add a flavor that does not exist with guitar.
Basically I think you need to think of the sound as a band, the keyboard player should play in a way the complements the other instruments, as should the guitar player. I think that the best way is to work with orchestrating whatever you have to minimize the need of applying EQ in the mix.
Not that I succeed in this but it is what i strive for....