Plenty of people have been able to successfully blend ported and sealed subs, but it generally takes a lot of work. As Craig John notes above, there are many factors that should be weighed when deciding what to do, and how to get it done properly. In some (many?) cases, this work isn't done, and the resulting system is less than the sum of its parts. As such, I generally tend to discourage people from blending dissimilar products if they are not well versed in the process, or lack a desire to measure + tinker + measure +adjust + measure +move items + measure + adjust again + measure +move items again + measure +...........+ measure, and enjoy the process while they are doing it.
In your case, I'd look at the PC13 for a similar price ($1699) of the SB13U, and check their outlet specials to see if one comes up there for about the same price as the SB13. Shy of that, the ported Plus has a similar roll-off, tuning, and close output levels, so that would be plan B.
Augustine's Law: "The last 10% of performance generates one-third of the cost and two-thirds of the problems."
"If it works the first time, it's not high end." ~ Harry Pierson