Having lost Alejandro Galvez to Werder Bremen on a free transfer last month, Paco Jemez has brought in Ghana international Boateng and former Rayo man Amaya.
Boateng has signed on a one-year deal, having endured a tough season-long spell at Premier League club Fulham.
The former Getafe player featured in just five games for Fulham in a turbulent campaign that saw three different managers in charge at Craven Cottage before the club were eventually relegated.
The 31-year-old is joined at the Estadio del Rayo Vallecano by Amaya - who played for the club regularly between 2003 and 2009 - and he has agreed a two-year stay.
From there he moved to Wigan Athletic before returning to Rayo on loan and later signing for Real Betis, who now reside in the second tier following relegation.
He returns to Rayo after three years with Betis and the experienced defender will be tasked with helping to improve on the club's 12th-placed finish last season.
Rayo finished five points off a top-half finished thanks to three defeats on the spin at the end of their campaign.
