I’m not sure there’s a distinction between “liquidation” and “sale” preference. They are usually one and the same. In any case, the justification for awarding these preferences is to avoid exactly this situation from an investor’s POV.
Why would you take $1M from someone last year and sell for $1.7M this year and call it a long hard road? You took the money to grow it and sell it for more than that. I don’t blame them for being disgruntled, and it also sounds like you’re getting a crap deal from the acquirer.
This is an entire discipline, and you can spend accordingly. For what it’s worth, your brand is not just your logo. It’s your meaning to people who interact with you – in your logo, yes, but also your colors, fonts, voice, tone, taglines, ad creatives, social media presence, and so on. It should be reflected throughout your websites/apps and product experiences.
An agency can help you navigate all this, and a good one with start with brand strategy - ie, who is your target customer, and what is your promise to them. Getting advice or hands-on help from a marketing person who has led this process before could be very helpful to you, even if you do end up hiring an agency. Otherwise you’ll just end up with a deck.