The mid-bass woofers do have the grills, the horns do not need them.
If your goals are to have a system with a primary focus of projecting to wake range, then you need to go with an HLCD (Horn Loaded Compression Driver). A traditional coaxial speakers, like you have linked in your opening post will not get the job done as efficient as an HLCD. The Kicker KM6500.2 HLCD tower setup, whats pictured above, is a pair of 6.5 Continuous-cone mid-bass drivers and a pair of horns. With the right power, these can and will project music to your wake-boarder. Due to the continuous-cone mid-bass driver, component style horn, flare design and cross-over design, these yield a far warmer near-field sound quality then most other 6.5" Pro-axial HLCD. A Pro-axial HLCD is one with the horn flare through the center of the mid-bass cone. If you already have a 4 pod setup, these are an option worth looking at as they are sold as a raw driver. Kicker does offer pod options as well.
With the horn and mid wired together in parallel, the nominal impedance (load) at the amp is still 4 ohm. This makes it ideal to run this setup bridged on a 4 chnl amp. I like this setup driven in the 200-250 watts rms range.
The kicker setup sounds like a great option for you. I'd either go that route or 1 pair of at least 8 inch hlcds whether it be exile xm9, bullet hp770, Wetsounds rev 8 or 10.
Does any one run Roswell setups I was looking at those new neptune8.0 wondering if they would work for wakeboarding