Interesting subject!
Basically I'm a guitarist (metal, death, black, what a surprise! LOL) and I've been playing (as an amateur) for 30 years so I have dozens and dozens of riffs and compositions in reserve. So for a few years now I've been adapting my metal riffs and compositions to make them into songs without guitar, using a synthesizer (VSTi).
I never had any difficulty to compose, because I always have several ideas in mind and an overflowing imagination. What is difficult for me is to limit myself and to simplify (my too many riff changes) my compositions.
So, the few times I don't have an idea, I just start a percussion rhythm (simple and repetitive, just to have a beat, a "hypnotic click" to play) and as soon as I put my fingers on my guitar and/or on my MIDI keyboard, I just play notes from the natural minor and/or harmonic scale and after a minute or two, I naturally "find" something, a theme, a melody, etc. It comes naturally, as if I were "magically infused".
I don't believe in magic (in the paranormal sense of the word), but playing "random" notes from a specific scale over a rhythmic pattern creates a kind of "
emergent phenomenon" where I am inspired by what I hear (play)... ...which affects what I play in return. In short, it creates a kind of "
feedback loop" where I influence and inspire myself. It's hard to explain, but in scientific terms "emergent phenomenon" and "feedback loop" are the terms that best describe what happens for me.
In short, my advice to anyone lacking ideas or inspiration is to use a simple hypnotic percussive beat (whatever the BPM, as you wish) and start playing anything within a scale (the one you prefer). After a few minutes, hearing notes (that you play) will "magically" inspire you. At least, it works for me. I may eventually make a video to show how I do it.
Otherwise, I have several DAWs (Studio One, Reaper, Mixcraft), but to do DS (or similar, or orchestral), I use FL Studio because its piano roll is the most efficient (for me) and I like to create in "pattern" mode and then structure everything at the end by putting some patterns together.
Concerning VSTi (virtual instrument~plugins), for what is DS or similar, I own and use :
Roland Sound Canvas VA (my favorite because it doesn't consume a lot of resources [CPU] and the sounds sound typically "DS". I love it!)
Roland JV-1080 &
XV-5080 ( it's like Sound Canvas, but with more editing possibilities. On the other hand it consumes a bit more CPU)
Roland
SRX ORCHESTRA &
SRX STRINGS (like Canvas/JV/XV, but focused on orchestra and strings sounds! They sound very "DS" too!)
KORG Collection - TRITON ( it's the equivalent of Canvas/SRX/JV/XV, but from Korg. Great sound for DS. But I prefer the "colors" of Roland sounds).
Image-Line Sytrus (native VSTi included with FL Studio. It's the ultimate FM synth! I love it! Infinite editing possibilities!).
But because I know Kontakt (I do some simple KSP scripting in the past), I sometimes, for example, combine several sounds from the VSTi's mentioned above, in order to do some "layering/stacking" to create a "combi", a "personalized sound" that I sample to make a Kontakt sampled instrument! So I have string, brass, pad, and choir sounds that are actually made up of several layers of sounds from some VSTi's. This gives me custom sounds that are a bit different from the basic VSTi presets!