Interesting. For me it was quite the opposite: I was using softsynths (mostly NI Komplete) for several years, but was mainly looking for presets that fitted to the music. And although I am interested in sound design for decades, I rarely tweaked those presets, and even less often I created something by myself. Most of the time I was overwhealmed by the plethora of available presets and the complexity of the softsynths.
It wasn't before I bought my first hardware synth, a Moog Sub37, that I started to create sounds from scratch. There's something about the simplicity of a high quality monophonic hardware synth that helped me to dig in: The reduced set of features, all those knobs that scream to be tweaked and a sound that is great from the start even with a single sawtooth. That synth really helped me to understand the basic ingredients of synthesis and how to put those ingredients together to acheive certain results. That experience was so positive, that I soon wanted polyphony and more features, which I found in the Virus.
What helped me then, and still helps me are:
- YouTube videos on synthesis and sound design. Even if they are about a different synth than the one you want to use, or about a different sound aspect than you're currently interested in, you always learn something for later and may run into a bit of information that can help you in a different situation.
- Whatch or read more technical oriented information. It can help you to acheive sounds that might be impossible before. Just a tiny bit: A delay, a chorus, a flanger and a comb filter are essentially the same but allow to adjust and modulate the delay time differently. So a delay which allows to precisely adjust very small delay times can act as a comb filter, and one that allows to modulate the delay time as a chorus. This technical knowledge comes in handy if you want to get a certain sound but your synth is missing the obvious element: Maybe you can tweak some other part to behave in the desired way.
- Analyse presets which you like. How are they made. What waveforms, what filters, what effects do they use. What happens if you change one of those elements.
- Recreate sounds you like (from other synths). By doing that, you have to dissect the original sound either literally if you have the (soft)synth in question and can check out all its elements, or aurally by trying to identify all the elements and recreate them.
- Emulate sounds of other instruments as closely as possible, even if you have no intention of using them. It sharpens your skills of analysing and synthesizing, and might give you new ideas on how to acheive something. For example: The last couple of days I tried to emulate the Vox Humana sound on the Virus, and I'd never have thought that the crucial piece to match that sound is the LFOs.
- Spend lots of quality time with your synth (yes, only one at a time). Get to know it. Get to understand how you can work around its limitations.
A great resource to get deeper, especially on the Virus are the tutorial videos offered by Access Music. IMO, Ben Crosland is a great sound designer and a great teacher. That's about it. For now.
Hope that helps!