The sound of music lost for over 300 years was heard for the first time in Chirk Castle chapel on Saturday.
The manuscripts were copied in the 1630s, and remained undiscovered at the castle until the 1960s.
They were bought at a Sotheby's auction by an American bidder and remain in a New York Library.
A lecturer from Bangor University has led a team which has spent the last five years transcribing the pieces into modern-day music scores.
The manuscripts are considered to represent the best, and possibly the only known, example of 17th century Welsh church music.
The pieces were copied in the 1630s by William Deane, who was the organist for both Chirk Castle and the Wrexham Parish Church.
More than 300 years later they were discovered in Chirk Castle before being sold at auction.
Dr David Evans and his team of researchers from Bangor arranged to have copies sent over from the United States.
They discovered that 20 of the pieces, including works by leading 16th and 17th Century English composers, were completely new discoveries, and had only survived in the Chirk collection.
"It was rather like finding unknown pieces by Bach or Mozart or Beethoven," said Dr Evans.
The team of researchers had to transcribe the manuscripts
"We realised that if we were going to increase our understanding of music in Wales in the early 17th Century that these music books ought to be transcribed... and we have actually found some quite good material, some really interesting treasures."
Dr Evans said the manuscripts had to be transcribed as in the 17th Century each individual part was written in a separate book.
But despite the historical significance to Wales, Dr Evans is doubtful they will return home as he estimates they are worth around £50,000.
But in musical terms, he says, they are priceless.
"They're priceless for the musicologists because they open up a new area of knowledge," he added.
"There are so few music manuscripts left here in Wales now that they give us an excellent view, so in that sense they're also priceless."