well for the most part amplifiers take an analog signal. while easy for your computer to output with a soundcard the ps4 i am not so sure of. this is why i said you may need one with either an integrated dac or a dac (so you could spdif from two sources).
while true that avr can be somewhat large not all of them are expensive. i personally use a pioneer and it is great however i'm not sure what they have in your budget. i've heard onkyo is good for a low budget.