Running a preamp into another preamp

That's above my pay grade.

Whoa, 
I would try PM'ing Ralph Karsten (atmasphere).
I do know he has experience with recording, as well as experience with building stereo equipment. Plus, he is a nice guy who can explain things in terms we mortals can understand.

Bob

Normally I'd say you need a mixer. But the Sony it seems is the mixer. So okay. Rock on!

I blew some hifi speakers out trying to play guitar through them. Its possible they weren't up to the task, but I think you want PA speakers for this. I would run your Sony output to a mixer, guitar into another mixer channel, the out to some pa speakers.  It also gives you way more flexibility imo.

I’m not able to follow completely, but I know you can run one preamp into another because that’s exactly what I do for my stereo.
I have a McIntosh MX110z, which has a limited number of inputs, so I have a Kenwood Basic C2 preamp (which is where I have the TV, CD player, and a couple of other things plugged in), and I use the "Tape Out" output on the Kenwood and connect it to the the "Auxiliary" input on the McIntosh.
The key is having a "Tape Out" output for an unamplified output from the first preamp, but maybe you don’t have that (and maybe I’m completely off the mark since you are talking about music creation instead of reproduction).
Anyway, good luck.

It's all just gain. Like was said above, you need to be careful you don't have too much of it or you can make your amp clip and/or break the speakers. But as long as you're not pushing too much power you should be fine. 

Yeah it’s a pretty small room in an apartment with neighbors on the other side, so I’ll be playing at a pretty low volume or through headphones. Also, the speakers are rated at 300 watts each and the amp is only rated at something like 100 watts/channel so I think it should be fine. Thanks everyone

Ok, It's been about 20-30 years or so but- 
 Me and my friends found the easiest way to do this, "At least back then"., was to use a, "Cassette Deck", which everyone had back then. Any cassette tape deck will work for this. But the quality of the deck and also it's "function list" can make a huge difference. "Especially when playing with recorded media from other studio's". All the good decks always had individual channel, "gain leveling" adjustments also. One of the best and definitely the easiest way we found was with a certain, "Teac" dual cassette deck actually. Using the "Tape record-In", "RCA" inputs ", "R+L", or "Single channel".  Because that particular deck had a playback tape, "Pitch control" for each channel. That will allow you to bring what-ever the music you are playing into tune (exactly) with your guitars tuning. "I always tuned with a "fork" or at the very least a "Banana", but it never seemed to matter. The recordings, even my own  were always off a bit somehow. "Even the minutiae of an in -house voltage variance can do this". Like a reading of "115V" as opposed to say,"117V" in a residential system. That pitch control makes it ALLOT easier to play (with) a recording. Or else it seemed like you would have to 're-tune the guitar every time you changed recordings or you would be off at least a bit. "Have you ever tuned two guitars together, to play a song live like say,-(Black Sabbath)"? Both guitars have to be tuned (exactly) against each other or else it just doesn't truly sound right. But when we were on it? Man it sounded amazing!
A trick for that is to tune normally, THEN, tune one, "Harmonic" against the same on the other guitar. That was the only way......
"Try playing the intro with the two, "Fretless", guitars to, "Cat Stevens", "Take a walk on the wild side" without doing that!
 You can then also use this set-up to record any changes you make to a song by just recording your throughput along with the other recording. while it plays on the primary side of the "Teac" deck on a blank cassette  in the "Teac", in real-time.
 From the instrument itself, you "can", plug directly into the deck with an 1/4"-TS to rca, splitter/adapter. But your sound and gain will be quite "Hokey". But you can try it. This depends mainly on your, "Pick-ups". And back then "Active pick-up's" didn't even exist, "so your on your own if you have those".
I am now remembering, "As the cobwebs are getting knocked off a bit".-
About the transition from any guitar with a pick-up, "acoustic or electric" to the cassette deck or reel to reel. First you need a 1/4"-T.S. to a two channel, rca splitter, adaptor.  
"NOT a 1/4"-TRS, to rca, adaptor"!
Unless you have a stereo-out guitar?? You do not......
 You can "depending on the gear", use certain, "Effects pedals". Like a decent "BOSS", "EQ" pedal with gain adjustment. My favorite and best sounding way was to use the, "BOSS, 2 channel, Digital delay", (The one with the three 1/4" outputs and two 1/4" inputs). But that "can", be problematic depending on the gear. Simply, "Too much" or a set-up wired or grounded incorrectly = noise. "Ended up with a Roland GP-8/FC-100", and an, "Alesis", "Midi-verb". Plus the two "DBX", 32 band Eq's and not much else.
As a standard, in my "Reference", set-up rig. At the end of my effects rack. I used two "DBX", analog, "32 band, EQ's".
(One per channel, R+L). And before "ANY" amplification. Using the secondary 1/4" outputs on each EQ into either the stage's mixer being used or at practice or home into a mixer, reel to reel or that "Teac" deck with a 1/4" - RCA adapter. And the primary outputs into my main 100W heads- "Randall/ Mesa boogie".
That was the best sounding way.
 So that's my two cents about the easiest way. And it took years to figure that out.

 I also have done this through various 4, 8 and 16 track, "Analog tape" recorder/players.
 I hope this helps....
      And, "Merry Christmas"!