IMHO, after 40 + years of experience playing both bass and violin:
1. Play more simply (less busy). Huge things (like heavyweights) don't move like flyweights. May be psycho-acoustics...but it works! This also gives acoustic space ("air")around the notes, increasing the perceived size of the music. As well, you are less likely to muddy or crowd low frequencies that give the sound mass.
2. Rick is absolutely correct! Play at lower volume/sound pressure levels. This requires great touch because playing flaws (string noise, other signal to noise problems) will be magnified by the boosting of the signal necessary to achieve actual "loudness" (as opposed to the usual attenuation of the incoming signal).
3. Record in the appropriate room...a little, weany, dry space will not let the sound bloom naturally. Yes, one could use ambience plugins, etc---but the resonance of the recording space can really inspire HUGE sound and will influence the willingness of musicians to do steps 1 and 2.
4. Playing style--I have used a baritone violin (regular fiddle with thicker strings tuned an octave lower). By using little or slow cello-like vibrato, the ear hears it as being larger than the frequently thin, rapid, warbly vibrato used by many violinists. Check out the huge sound of Allison Krauss and Darol Anger--neither one plays loudly, but both use vibrato sparingly.
In the classical world, check out the solo Bach partita and sonata recordings of Sigiswald Kuijken who uses almost no vibrato at all. They sound immense.