The low B, at about 32 Hz, is hard enough for the bass to produce at the same amplitude as the other strings but the speakers need to produce a lot of energy in that range. In a small space, it's not so hard but in a large room, even response it harder to achieve. As you mentioned, frequencies below the port tuning causes problems and if you don't know exactly how a port works, here's a simple explanation- blow across the top of a bottle and listen to the note, then add water and listen to the change in pitch. You have just re-tuned the bottle by shortening the length of the cylinder. A port operates best at one frequency- its tuning frequency. The volume of any notes it may produce is greatly reduced above and below that frequency and all a port is designed to do is help to extend the low frequency response. It's tuned below the sealed box's effective range and is supposed to be tuned so it blends well, i.e., the speaker/box's -3dB point and the port's -3dB point just about coincide and don't cause a noticeable bump unless it's A) needed, B) wanted or C) won't cause a problem. Below the port tuning frequency, it acts like an uncontrolled leak in a sealed box. Because a port works well at only frequency, the rest provide some resistance to the cone's movement but below, it can shake itself apart through over-excursion. It's pretty ugly when this happens.
If you want to use this tuning, find drivers that work well at low frequencies in a sealed box and make the box as rigid as possible. No leaks can be tolerated, at all. A minor leak in a sealed cabinet is a really bad thing for the tuning- if you have a small leak, you might as well just drill holes and make it a large leak. some amps, like the Peavey IPR series, have sub-harmonic enhancement but I wouldn't recommend using that with a ported box that is tuned higher.
BTW- the amp should be able to handle 27Hx- it's stated frequency response and distortion specs should go down to at least 20Hz but if you play double-stops, the difference between the notes can produce notes that are below 20Hz. If you use harmonics to tune at the 5th fret, the slow pulsation just above and below correct tuning is called the "beat frequency" and it's the main reason amps sometimes have a subsonic filter.
