Re: tape over tuning-port ...
I tried something like this quite a while back. Did not like the results (it just doesn't affect bass (which to my ears becomes too light) ... mids become way too beamy, etc.). You can go part way by perforating the tape with a pin -- but even this is ruinous to the orig sound.
The IE8 was not designed for acoustic suspension -- it's a damped/tuned/bass-reflex system. While I think the low end can't be dialed as far down as I'd like, plugging-up-the-port approach is not a way to correct the issue. To sound optimal, the dynamic transducer inside the IE8 has to breathe ... with its genetic mouth/nose.
All that said ... this experiment may be valuable in demonstrating the fundamental design limits of the stock IE8: that Senn (or a cloner or sophisticated modder) may need to re-engineer the basic design -- in a proper science laboratory, with purpose-built dummy-heads and powerful data-acquisition equipment. I'm sure Senn., and other electronic giants, have these labs.
IAC, and given its limits*, and among the models I own or have sampled, the IE8 is still the best IEM I've heard to date.
* IE8 cons include: tubby bass; poor isolation; not-as-detailed overall sound as other top uni's (e.g., ER 4S). IAC, I would not trade bettering these any of these cons if any of the IE8's orig pros were sacrificed.