My advice, other than using/designing good sounds of course, involves some easy production ideas...
In a combinator:
Double/triple up your synths with the same initial file and then tweak each of their controls so they aren't all playing exactly the same thing but are now complementing each other.
Submix your synths
Use a splitter/merger from the submix and then add that to another submixer
split the channel three ways and pan left, middle and right. This will instantly widen and fatten your sound.
You can also use the stereo imagers to treat different parts of the spectrum of the synth differently.
From your second submix split the signal again. Take a dry signal back into a third submix and then try taking some lines into other processings. So I like to take a second line into a stereo imager, high pass it effectively by soloing the hi - band and setting the khz and then maybe boosting the top end a touch with the eq and then add a little reverb. This gives the top end of your synth some sparkle without muddying up mid and bottom.
You could also use this technique to isolate the lower band and then effectively parallel compress the bottom end of the synth sound.
Bottom line, if you are treating each synth as a one synth to one mixer channel, this could help explain why things sound a little thin. Through merging, splitting, submixing, parallel compressing and separately treating sends you can take a pretty thin sound and make it sound huge.
Stuff like that.
You can also try the haas effect - there are tutorials online for that. But the idea is to add millisecond delays to your sound, not to get delay but to strengthen the sound, as it were.
Also, in your final mix, try things like the 8 band parallel compressor patch which produces a really huge sound. Maybe you know all this so sorry if that's obvious but they're just some thoughts.