Books about Capital Solutions Investing

Probably Mezzanine Financing by Luc Nijs? Otherwise I haven't heard / or I don't see the need to have an actual book for "hybrid solutions". 

I believe that Moyer already provides an foundational idea on hybrid investing, which is why those roles favor distressed/RX bankers. The capitals structure arbitrage idea from Moyer is easily applicable to hybrid solutions, in that you should have a no arbitrage when you decide to buy/lend a riskier tranche to a company i.e., the asked reward should match the risk you're taking and your reward should be priced higher > than senior claims and lower to equity claims if the risk is also in between those two tranches. 

I believe a much more relevant chapter, for lack of better books, would be checking books / articles pricing credit risk beyond the classic credit ratings / Damodaran model, which can be a bit harder for private companies given that you can't run comparables on public credit. The "reward" side for this risk is a negotiation point that you should always ask for the higest amount possible and decide what would be the floor at which you could settle. Hence risk should always be correctly quanitied, meanwhile the reward is floor-based and should always ask for the highest amount. This is why Moyer is also a good reference for hybrid because credit is focused on downside given they are fixed claims, which helps you understand what actual risk you're taking based on the potential recoveries you might get. Preferred equity is a bit more technical in that it's basically an option, so should be familiar with options pricing. 

Even Howard Marks has a memorable memo where he discusses that beyond all those "creative" capital solutions, at the end of the day when you remove all the lingo you either have a debt claim or equity. The lower you go in the capital structure, the higher the risk and hence the required reward.

The concept / idea is as simple as this. The reason why in practice it might look "complex" is that you can't adhere to lazy thinking like the 1Ls in that you know you might easily get +90% recovery in the downside even if you don't run any valuation/DD. The lowest you are in the capital structure the more you need to turn rocks around to find some additional assets/points that might make you more comfortable knowing you might still have an acceptable recovery / how much and how quick the company repaid you before defaulting on top of what you might recover (this last idea is similar to HY bonds being non callable for 3-5 years).