Can a professional do the things your floor guy claims? Yes. absolutely. My only advice would be don't just rely on him and his word. go get 3 or 4 more pros out to give their opinion and estimate for the work.

In "the olden days" ...preparing a strip wood floor for applying a finish floor over was something regularly done. This involved flattening the strip wood by sanding and then applying a sanding sealer (shellac). An asphalt saturated lining felt was glued to that and the finish flooring installed. We also used mineral fiber lining felt on occasion and in the recent past we used a cushioned lining material by Tarkett, which could be loose layed. Also 1/8" cork can be used in such an application. All these options provided a flat and secure substrate for new resilient flooring. It can been used successfully by a skilled flooring professional. In my opinion, sheet Marmoleum can be successfully installed by this double bond method, although you would need to check with Tarkett on that and find a certified installer.

Traditionally a nail-down "wide plank" hardwood receives "glue assist". That is to say glue is applied to the back of the planks and then nailed into place. Your problems will be SHRINKAGE due to VERY DRY conditions. A wide plank is VERY tricky to install in DRY climates such as yours. And to be clear, "wide" is anything 5" or wider. Your 7" wide planks are VERY wide. The wider the plank, the MORE it will shrink. The more it shrinks the bigger the gaps (where water and urine can fall into). The more it shrinks the unhappier you will be. A solid, narrow strip hardwood (such as 3" wide planks) would be the best option if you want wood. Some of the worst shrinkage/splitting/checking occurs in DRY climates. Humidity is SUCKED OUT of the wood so quickly it starts looking like 20 year old cedar shakes. Please check to see if you can ADD humidity to your entire home at the touch of a button (whole home humidifier). If you do not have this device, I highly recommend you purchase one. I would suspect $6K should get you what you need - but that number is highly dependent on size of your home and the type/size of your furnace/duct work.

If you are on slab, I'm not sure what you would be nailing TO. Adding in a sleeper subfloor would be very expensive and will still require a vapour barrier underneath. *Technically a glue down SOLID hardwood can be done on slab - but it isn't recommended unless your HIGH END flooring installer has done it successfully in the past. A glue down engineered floor is technically "more stable" in the widths they are suggesting, but I would question a comparison to a 2.25" solid hardwood. Especially if the solid NARROW strip hardwoods are rift or quarter sawn. The same adhesive would be used regardless of plank structure (solid vs. engineered). The RIGHT adhesive (aka. EXPENSIVE glue) MUST be used over slab in TX. And then the proper SPREAD RATE must be used (lots and lots of the expensive glue will be required) as well as the PROPER TROWEL profile/depth will be required. These expensive adhesives ($100/gallon is common) will achieve 30-50sf per gallon. These adhesives will be the vapour barrier. The most expensive ones will have "limitless" moisture content as one of their key features. Even with the TOP adhesives, the installation will still be cheaper than a sleeper subfloor + nail down installation. The sleeper subfloor would mean a lower priced flooring professional can be hired to achieve the nail-down installation. The glue down method will require the higher skilled professional with all the knowledge required to install a glue down wood floor PROPERLY. And the next issue is the HVAC system. Regardless of the installation method, your HVAC will have to have the ability to maintain a CONSISTANT level of humidity. Sometimes A/C isn't enough in high-humidity environments. Sometimes a whole-home dehumidifier is required in extreme humid areas. Please review your HVAC system's abilities to TIGHTLY control humidity (somewhere around 40% is PERFECT...and it must be maintained 24/7 for the next 25-60 years). Start there. Spend more money for the upgrade on the HVAC system so you can have the wood floors - regardless of width/composition.