You can actually use the volume column to some extent with soft synths: Volume Column + Vsti? - #2 by BYTE-Smasher
If you want to turn the synth sounds you make into samples you can use the plugin grabber, just right click the instrument in the instruments list. You can make single sample instrument or multisampled ones. I’m not familiar with the VST requirements on mod archive, but this way you can eliminate VSTi’s completely in your track.
I’ve noticed sometimes the rendered samples aren’t identical to the sound from the soft synth though, so i suggest rendering to a new instrument instead of overwriting the synth. I’m not sure why it’s not always identical, but i suspect it might have something to do with incompatible internal automations in the synth or differences in sample rate and bit rate.
If you haven’t checked these out yet i would recommend the free VSTi’s surge and zynaddsubfx(the early open source version). Both are very versatile and sounds great for free synths.