SX are budget guitars imported to US by Rondo Music, Union New Jersey.

From the SX web site:

As a brand, SX was only created in 1998.

Rondo┬áhistory with guitars began in early 1960s. It’s just another story of the great manufacturing industry migration. When guitar manufacture migrated from the States to Japan, then to Korea, then toTaiwan, we got the chance to found a guitar factory inTaiwan, making guitars for many prestige brands around the world. The factory soon became the biggest guitar factory inTaiwan and also became the cradle of numerous Taiwanese guitar makers (who learned how to make good guitars when they were employees of the company). During that period, we learned how to make good guitars and also built up knowledge for the guitar culture.
In the 1990s, when making guitars in Taiwanbecame cost prohibited, we established a new company, Team International Music Co., Ltd. It started as a distribution company, exclusively distributing many world famous brands (including Martin, Gibson and may others) inTaiwan till end of 2009.
In 1994, we sensed the great potential for musical instrument business in China and we formed Team China with several friends to venture into the surging Chinese market.
Team China at that time was only a trading company and it aimed at offering sourcing, quality control and shipping service for other western companies. With the advantages of more than 30 years successful guitar manufacturing experience and our profound understanding of the Chinese culture, Team China instantly became an enormous success. Our customers included many of those top guitar brands nowadays.
At that time we also tried to sell guitars with our only brand name. Sometimes we still got consumers sending pictures of guitars with Team logo, asking about info of the guitars like production date, prices, etc, etc. It is always so funny and heart warming to see those old guitars we made.
However, Team is the company name, really not a suitable name on a guitar. So in 1998, we decided to launch a new brand. One of the shareholders of Team China, Kevin Hague from Australasian Music Supplies Pty. Ltd, the No. 1 music distributor and wholesaler in Australia by volume sales, came up with the name Essex. Without a second’s hesitation, the name was decided.
To our surprise, soon after we released the products to the market, we discovered Steinway and Sons had registered Essexfor a new line of pianos almost at the same time. Then Essex was abbreviated and thus SX was born.
Within very short time, SX had become extremely popular as being the best valued guitar on the market, with unbeatable quality for the money. In 2003, we stopped taking OEM orders to focus on SX.
Again in 2009, we closed distribution business inTaiwan put all our resources on the fast growing SX business.

SX Guitar and Bass Catalog 2012