Anyone else have an opinion on whether u need a separate amp for these?
i've never heard your receiver or these speakers. but the speakers are not the most efficient speakers in the world. and your receiver is not the most powerful. however, as i understand it, you are already using the built-in x-over in the receiver to hi-pass the signal going to the jbl's. so that relieves them and the receiver's amp of some stress. the rest depends on how loud you listen, the size of the room, how far away you are from the speakers. ie: its rating at 87db/1w/1m means if you listen 4m away, it will take 32w to do 90db at that distance - which is pretty loud. but still within your receiver's rating. but it's getting close to its max - 64w needed for 93db. and marantz doesn't say what its peak power is; only rms. (i'm assuming its power rating is rms, marantz doesn't specify.)
from a speaker/amp safety perspective, if you turn it up as loud as you ever listen, and nothing is amiss, you're ok. from a sonic perspective, the sound might improve. i'd suspect it would; how much is another question.
if you're buying used, it's not as risky from a financial standpoint, as you can sell w/o taking a big loss, if it's not to your liking, and/or worth the cost to you for what may turn out to be only a small improvement. if you're going to spend a decent amount on something like the new rotel that you mentioned, if it were me, i would be wanting an extended in-home audition from a dealer before i pulled the trigger on a purchase. the aiyima amps i mentioned, however are so inexpensive that i'd not hesitate to buy them new - you could literally throw them away if you didn't care for them and not lose as much money as buying a new rotel, and then selling it if you don't think it's worth it. and, my experience w/them is they made a nice sonic improvement for me, over some high quality amps; and others have had the same experience.
after i finished writing the above, i then found amir's review of your receiver here on asr. based on that, i would highly encourage you to buy the aiyima a07 max (or a pair and run them bridged. not sure how you can hi-pass your monitors if you use the pre outs to power another amp, tho... not sure, even what the pre-outs do at all; no info in the manual. and, it seems the subs, even tho you can connect two, are mono? and after looking at the asr review, and further investigating the marantz manual; honestly, if it were me, i'd have never bought this receiver, and if i owned it, i'd be getting rid of it. no offense, but it seems like you need to get something more suited to audio, as well as being able to do h/t. whatever amp you get to use with this marantz, it will likely be running full range, w/no way to use the receiver's hi-pass function on it. and your subs are probably running mono. and if you ask marantz, you probably won't get any answers, as they probably don't know - just like they couldn't tell me what the crossover slope was.
your only other decent option, imo, if you want to keep this receiver, is buy an active outboard x-over and another amp (or two); run the marantz's pre out to the x-over, hi-pass goes to the new amp driving the jbl's; low pass goes to your powered subs - either into their lfe inputs, if they have them; or with the outboard x-over set at +/-80hz; and the powered sub's crossover set at their highest setting. based on everything i know about this receiver; from amir's measurements, and marantz's lack of useful info, an outboard amp and outboard x-over
will be a worthwhile sonic improvement. or just keep what you have, w/the marantz's internal amp driving the jbl's >80hz, and the low pass output driving your subs in mono. at some point, tho, i'd imagine getting a better avr receiver would be worthwhile, and then you could still use the beter amp and outboard x-over...
re: the cheap aiyima amps, i just finished fabbing a cover for the aiyima a07 max where i installed the $30/pair discrete class-a op amps, and i'm a happy camper.
system (2nd pair of subs ~20' behind listening area):
doug s.