Rene wants to use Bluetooth speakers to listen to his stereo, but his stereo doesn't have Bluetooth capability. He could find a cheap transmitter on Amazon that would use an analog connection to his stereo. Leo recommends the Azeca BT005 Bluetooth Transmitter for around $28. This would plug into the headphone jack of his stereo. He should know that the range for Bluetooth is only about 30 feet. If he needs a longer range, he may want to look into the Nolan TRX HD Bluetooth transmitter for around $100 on Amazon. Then Rene can either get Bluetooth speakers, or he can get Bluetooth receivers to connect to his existing speakers to simply make them wireless.
Chromecast Audio is an option Rene may want to consider as well, even though that is more for connecting his speakers to the internet. It's $35 and would plug into his speaker and join his Wi-Fi. Then he could use his smartphone to play audio to the speakers.
A more expensive but more reliable option is Sonos speakers. He would connect a base station to his stereo via optical connection, and then he'd also connect it to the internet. Then it can not only play his own music, but it could play from the internet as well.