[spiel2001]

The top bar is the main action bar and all of the buttons work together as a group. There's no direct way I can think of to split it into two bars unless you just want to put the bar on two rows instead of one. That you can do easily. Look in [ Interface > AddOns > nUI > Layouts > Default > nUI_Layout_Default_Dashboard.lua ] and locate the nUI_DefaultConfig.ButtonBars section. The one we care about is ["nUI_ActionBar"]

You can make it two rows of six columns by making the change indicated here...

    ["nUI_ActionBar"] =
    {
        btn_size = 53.5,
        gap      = 2,
        anchor   = "BOTTOM",
        xOfs     = 0,
        yOfs     = 123,
        rows     = 2,
        cols     = 6,
        page     = 1,
        nuibind  = "nUI_ACTIONBAR",
        binding  = "ACTIONBUTTON",
        label    = nUI_L["nUI_ActionBar"],
    },

As for the key bindings... you can just mouse over the button and ctrl-alt-right-click to set the bindings.

And, no, nUI does not do chat sounds, so you would want to reinstall that if you like that.