1:
When we studied Tractate Sotah we saw that there is a mishnah which gives a list of all the ritual recitations which need not necessarily be recited in Hebrew, but which may be recited in any language. Among them was Birkhat ha-Mazon. You can find the original explanation in Sotah 071, explanation # 11.

2:
The Gemara [Sotah 33a] attributes the fact that Birkhat ha-Mazon may be recited in any language to the fact that when the Torah introduces this mitzvah it does so in what appeared to the sages to be general terms:

But surely, this is just a peg upon which to hang the much more subtil idea that gratitude to God for having provided for our sustenance should come from the heart, and this can only be guaranteed if we can express our gratitude in the language most convenient to us.

3:
But even if Birkhat ha-Mazon was originally intended to be a kind of spontaneous expression of gratitude, it gradually became ritualized. By the time we reach the 17th century we find a very famous posek making only a grudging admission that Birkhat ha-Mazon may actually be recited in any language, and emphasizing that Hebrew is much to be preferred. Rabbi Yo'el ben Shemu'el Yaffé Sirkes [1561-1640], in his commentary on the Tur, Bayit Ĥadash, writes

Nowadays it is most customary to recite Birkhat ha-Mazon in Hebrew.

4:
Birkhat ha-Mazon must be recited out loud. While that does not have to be taken quite literally it certainly does rule out silent reading - i.e. eyes only. Silent reading of Birkhat ha-Mazon is permitted only in cases of great illness and other dire circumstances. However, recitation out loud does not necessarily mean that one needs to raise one's voice: it is permitted to "mumble" the words. That is to say that one may enunciate the words with one's lips even if one cannot hear what one is saying. Even so, it is preferable not only to enunciate the words but also to whisper the words so that we hear what we are saying if circumstances permit.

5:
Let us ignore the fact that paragraph 3 of Section 185 is couched in language that today would hardly be considered 'politically correct'. Even Rabbi Karo is a child of his time. The thrust of what he says is clear: when a family dines together it is best that one person recite Birkhat ha-Mazon out loud, with the rest of the company joining in. It is true that Rabbi Karo encourages this manner of reciting grace for the benefit of the children and womenfolk who might not be able to recite the grace themselves but but answering 'Amen' to the benedictions of the leader they fulfill their duty. However, one prominent posek from the 18th century [Elia Rabba] says:

There is, to my mind, nothing more guaranteed to evoke Oneg Shabbat - Shabbat joy - than when all those seated around the Shabbat table sing Birkhat ha-Mazon with fervour. This is the very essence of the sanctity of Shabbat from the psychological point of view. Decorum-shmecorum - just sing from the heart.

In our last shiur I posted a message from Yehuda Wiesen concerning recordings of z^emirot that are available online. After noting a couple of items that I had found I added: "If anyone can suggest more sites that fit the parameters set by Yehuda please let me know." Many more people responded to this request than I ever expected!

Josh Greenfield writes:

In response to Yehuda's query about audio recordings of zemirot, two sites come to mind: Virtual Cantor has recordings of 5 zemirot, plus benching and kiddush. Multiple versions available for most of the songs. Piyut.org.il has a phenomenal array of recordings, from various Jewish communal traditions. There are more than 20 recordings of Yah Ribon alone, and the site provides full texts in Hebrew, as well as commentary. For Shabbat songs, go directly to this page.

Joan Katz and Lawrence Charap recommend Virtual Cantor too. And Elro'i Sadeh enthusiastically supports the recommendation of Piyut.org.il.

Lawrence Charap also recommends:

Recordings from USYers and Cantor Jeffrey Shiovitz and Friday night melodies. He also provides a link to Camp Sdei Chemed international, which has put out two albums of Shabbat zemirot. He explains that each album has 2-5 versions of each zemer. They're available through www.mostlymusic.com and are very inexpensive. I would also mention a terrific CD by Rahel Jaskow called "Day of Rest" which has many lovely a capella renditions of traditional zemirot tunes - available for purchase at http://cdbaby.com/cd/rahel or from iTunes. There are a number of other sources scattered here and there on the Internet, but these are the best that I've found.

Jordan Wosnik is kind enough to make Yehuda a direct offer:

If Yehuda would like, I can make recordings of the zemirot you discussed (the ones that are not included on "Siddur Audio" - Ki Eshm'ra Shabbat, Baruch Kel Elyon, etc). I can put these in MP3 format and either send them to Yehuda or host them briefly on my own site.

Bonni Schiff writes:

We have two disks that have great recordings of the traditional Shabbat z'mirot: "Zemirot From My Father's House" by Cantor Gadi Elon and "The Zimirot-Sing-Along" (with accompanying book of words and musical notations) put out by Tara Music. These disks include Yedid Nefesh, Tzur Mishelo, Dror Yikra, Ki Eshmerah Shabbat, Baruch El Elyon, Yom Zeh L'Yisrael, Yom Shabbaton, Yah Ribbon, Yom Zeh Mechubad and many others.

Please note that I have not tested any of the above links.

Chanukah Samé'aĥ to everybody!