I had to try a couple things to see how this could work. Here is what I came up with….
First add this to your .site-header
on line 1975 in your Style.css file.
.site-header {
background: url(http://share.joychallenge.com/wp-content/uploads/2015/07/cropped-40day-logo.png) no-repeat !important;
}
Next, remove the width for .header-image .site-title a
on line 2045 like this –
.header-image .site-title a {
float: left;
min-height: 164px;
width: 0;
}
It seemed to work for me, let me know if it works on your end.