Newbie with some turntable, cable, pre-amp, and speaker questions.

I am very new to "higher end" audio equipment and I have a few questions for the professionals. I thought I bought a decent used system until I saw a pair of $25k speaker for sale on one of the pages here. By no means did I think I purchased anything "amazing" but those speakers were certainly a reality check! lol :) Wood cones?....wow!

I’ve always wanted a nice sound system for my house, nothing crazy, but something I can play pretty loud and not distort the speakers.
I ended up buying a used H/K AVR 7300 and some Polk LSi 15s, Center, and a RSW 400. Paid $675 for the lot and I’m pretty happy with what I got.
I definitely need to complete the surround and would like to find at least a set of F/X’s and possibly 7’s to finish it off.

This system is probably substandard to most, but for a newbie with my 1st decent sound system...I am absolutely elated with the sound I am getting out of what I have. I’m not sure I want to even listen to a very high end system as I’d like to enjoy what I can actually afford!

I have a few questions about some items I received with the lot and some accessries I am looking for.
I would like to add a turntable to the system, and would like to get some opinions on H/K models that would be best to match up with what I have. I don’t need anything super high end, but don’t mind keeping my eye out for the best possible one to grab either. I’ve also been told I’ll need a pre-amp if I want to add a TT...not sure why, but if this is accurate, I’ll need some advice there as well.
Also, the system came with Monster cables but the ends are cracked and are now useless. Does anyone know if they honor their LT Warranty to 2nd owners?

Finally, if anyone has a pair of LSi F/X’s...I am looking to buy a pair immediately. I’m located in North Western NJ.
Thank you all in advance for any info you can pass along. It is much appreciated.