Earlier quoted context omitted.
Where on earth would $40k/year be a reasonable salary for a "senior software engineer"?
You could live in a small town decently well for $40k/year, and 5% equity could be worth millions if it was equity of the non-toilet-paper variety (some dilution protection) and the company did very well. If I were to even consider such a position I'd involve a lawyer in examining the equity part, and I'd really have to believe in the company.
I can imagine a brand-new CS graduate settling for $40k, if they lived in a small town where living was cheap and jobs were scarce, but offering $40k for a senior position just seems insulting, no matter where the company is located.
CrystalMD would do better to offer $1/year for this job, since what they are actually looking for is an angel investor whose capital happens to come in the form of engineering time.