Aside from the main issue that we have in the source sheet שמא יתקן (lest one fix) and the secondary issue which is reflected in source #1 in the Yerushalmi עובדין דחול (doing as one does during the week) I want to enumerate a number of other possible obstacles. We don’t have time to examine each in depth but we should be aware of them.
1) טילטול ד’ אמות ברשות הרבים והוצאה מרשות לרשות
Carrying four amot in the public domain and carrying from one domain to another
Unless one lives in a community where there is a צורת הפתח commonly known as an ערוב eruv, it is forbidden, for example, to carry on object from one’s house to the synagogue. This is the reason why we do not blow the Shofar on Shabbat.
The issue is not insurmountable. As synagogues provide siddurim and tallitot to the worshippers they can also provide the musical instruments. As some people prefer to leave their own siddur or tallit in the synagogue, a musician can also leave his instrument in a locked room in the shul prior to Shabbat.
In communities or situations where fear of carrying is tangible, it might be a reason to look into having musical instruments on the רגלים (Passover, Shavuot and Sukkot) and Rosh Hoshanah when carrying is permitted (when these holidays are not on Shabbat). On Simhat Torah in particular, authorities have been more lenient about the possibility of clapping and dancing.
2) זכר לחורבן
Memorial to the Destruction of the Temple
After the destruction of the second Temple, the Rabbis enacted a number of measures to ensure that the people would be in mourning for the Temple. One of them was to ban music altogether, not just on Shabbat or Festivals. The Jewish people were never able to strictly uphold this ban. The stipulations were lightened or qualified over time. There are still some ultra-Orthodox Jews who will not attend a wedding in Jerusalem in which a band performs, but in almost all Jewish circles weddings are by and large identified with instrumental song and dance. For Zionists, the reestablishment of the state of Israel has provided additional reason to reinstitute music in all areas of celebration.
3) חוקות הגוים או “בחוקותיהם לא תלכו”
“The ways of the Gentiles” or “In their ways you shall not go”
When the organ was introduced into Reform synagogues in Germany in the 19th century, there was opposition to the effect that they were copying the practices of the Churches. One could also state today that the Jews have got the idea of introducing other instruments into the shul because of exciting or moving musical worship services that they have seen or heard about in churches. However, one could also state that originally in the Temple we had musical instruments accompany our rituals. This was way before Christianity. We are simply returning to our true selves.
4) חשמל
Electricity
This is, of course, a major issue. If electricity is forbidden, then the discussion can simply focus on the numerous non-electric instruments.
For those who permit electricity, we’d also have to ask the question are all types of electricity permissible including the machinery that accompanies rock bands, etc.
As I mentioned, I think the most serious issue is שמא יתקן lest one come to fix an instrument. The world was completed in six days and God rested on the seventh day. Everything was in place. Likewise, we want everything to be ready before Shabbat. The Rabbis placed “fences” around the Torah to ensure that one would not come to fix anything. Are these fences still relevant?