$500 is not much to work with but you gotta start somewhere. Only thing I can recommend in that range is a Pioneer speaker setup with a refurbished Onkyo/Denon 5.1/7.1 AVR or maybe an Onkyo HTiB, HTS9400/9500, because Onkyo uses real receivers in their HTiBs that can be added to/upgraded easily.
Denon AVR X7200WA, Emotiva XPR-5, Emotiva XPA-7, Sony XBR 75" 850C, Oppo BDP-103D, Roku 4.
DefTech BP7000SC (L/R), CLR3000 (C), SM55 (FH), UIW BPZ/A (SB), UIW 75 (TM).
JBL L7 (Sur), EoSone RSR 350 (RH).
PC 2.1 setup. Emotiva Stealth 6, SVS SB2000 sub, Emotiva DC-1 DAC.