OK, so I tried this last night, albeit not for very long as I'd promised to watch some tv with the other half.... anyway, my very subjective impression is that the sound is quite different, with a change in the quality and 'shape' of the bass response. If anything, I didn't feel it reduced bass so much as evened out the in-room response a bit. And, maybe, did I sense a tightening up of the attack of bass drum hits? Difficult to say; I didn't perceive the three-port setup as lacking in any way in the bass, other than there being maybe a touch too much of it. This is with two of the three ports bunged per side. I'll listen again later.
What might be interesting is to see if this enables me to dial back the HF energy a bit; I'd had to increase it in my room to account for soft furnishings and a sense of it still lacking a touch of 'air' with my amp, but mayhap it's a side-effect of having a little too much bass energy in the room. By which I mean, for a given listening level, a greater % of that sound spectrum was bass energy rather than treble energy; blocking those ports clearly reduces the amount of low and mid-bass energy by a few dB, in turn maybe moving the balance between low and high frequency sound 'in room' back towards something more even for that same perceived listening volume.
Anyway, it's very handy that the Ardens are configurable in this way, it opens up a range of 'room tuning' tweaks that can be experimented with to get the best out of them. I may even try all three bungs in, but I have a feeling two may be the happy compromise.