Question on Preamp Outputs.

I was hoping that you guys can answer a question.

My preamp, a Marantz 8802a has a max output of 2.4 volts balanced output. I am looking into a McIntosh Amp that is rated for a higher input potential. I am generally pleased with my Marantz. Below are the specs pf the McIntosh and the Marantz.

McIntosh MC462
Power Output Minimum sine wave continuous average power output per channel, with both channels operating is: 450 watts into 2 ohm load 450 watts into 4 ohm load 450 watts into 8 ohm load Output Load Impedance 2, 4 or 8 ohms Rated Power Band 20Hz to 20,000Hz Total Harmonic Distortion 0.005% maximum harmonic distortion at any power level from 250 milliwatts to rated power, 20Hz to 20,000Hz Dynamic Headroom 3.0dB Frequency Response +0, -0.25dB from 20Hz to 20,000Hz +0, -3.0dB from 10Hz to 100,000Hz Input Sensitivity (for rated output) 4.2 Volts Balanced 2.1 Volts Unbalanced

Marantz 8802a
Analog Input sensitivity/Input impedance: Unbalanced RCA input:200 mV/47 kΩ/kohms Balanced XLR input:400 mV/94 kΩ/kohms Frequency response: 10 Hz – 100 kHz — +1, –3 dB (Direct mode) S/N: 105 dB (IHF–A weighted, Direct mode) Distortion: 0.005 % (20 Hz – 20 kHz) (Direct mode) Rated output: Unbalanced RCA pre-output : 1.2 V Balanced XLR pre-output: 2.4 V 0 Digital D/A output: Rated output — 2 V (at 0 dB playback) Total harmonic distortion — 0.008 % (1 kHz, at 0 dB) S/N ratio — 102 dB Dynamic range — 100 dB Digital input: Format — Digital audio interface 0 Phono equalizer Input sensitivity: 2.5 mV RIAA deviation: ±1 dB (20 Hz to 20 kHz) S/N: 74 dB (IHF-A、with 5 mV input) Rated output: 150 mV Distortion factor: 0.03 % (1 kHz, 3 V)

Since my Pre has 2.4 volts , what does that mean in the grand scheme? Aside from getting a better dedicate two channel preamp .. I know I should, but that will come later. 

Thank you In advance.
You will get less than full power by using the Marantz's balanced outputs. About a bit more than 225 wpc into all impedances - the Mc462 uses autoformers on the output stages. Same if you used the Marantz's unbalanced RCA outputs. 
Here's the math: 2.4 ÷ 4.2 = .5714 × 450 = 257.14 watts into all impedances! 
People here will say "this preamp or that preamp" will sound "better"! They will claim that their "golden ears" told them this! The 8802 is an excellent measuring - and sounding! - preamp! Plus it has a phono stage - something lacking in many current preamps. I expect that the 8802 will be "transparent" to the source! Replacing it would be a sideways move at best!
The bad news is you can't get the max. rated output power from the McIntosh MC462.
The good news is the Marantz 8802a won't drive the McIntosh MC462 into clipping and in reality your speakers may not require that much power.

Here's the math: 2.4 ÷ 4.2 = .5714 × 450 = 257.14 watts into all impedances!
Power is proportional to voltage squared (2.4/4.2)^2 x 450 = 147W

I think that XLR/balanced outputs are over-rated! They are only useful if you need to run 10, 20, 30 ... feet cables! At one or two meters "No diffawrance" as the French chef said!
Ehh, why buy an amp with 450 Watts to only have the potential of 150? Plus Powergaurd won't let it clip, right? 
So why couldn’t you get a XLR to RCA adapter, from XLR out of the preamp to the RCA input of the MC462? Thus, giving 2.4volts to the unbalanced end of the amp? Does it not work that way? 🤓
@kijanki : you get an F! My math is correct! It is just a simple linear proportion comparing 2.4 to 4.2! And then multiplying the result by 450. You are thinking of watts -to- volts of an amp's power output. So way off the mark!
jasonbourne52  You multiply power by the ratio of voltage and that is wrong.  It is not linear problem since output power is function of input voltage squared.  For instance 1/2 of voltage = 1/4 of power.
Amazon has some adapters: GXR - 134 from zZounds for $8.65 each. However you may experience distortion when using an XLR/RCA adapter because they shunt pin 3 to ground at the unbalanced end. Pins 2 and 3 are out-of-phase signals. Some amps won't tolerate having an out-of-phase signal connected to their input ground!
I think you will really need an adapter using a transformer to avoid having pin 3 connected to the shield ground at the amp's RCA jacks.
@kijanki : so half of 4.2 is 2.1 volts. You say that the power in watts is 450 ÷ 4? That sounds way off!
 @kijanki : an amp producing 25 watts is actually outputting 14 volts. At 50 watts  it is outputting 20 volts. I understand this type of non-linear proportion. I don't think it applies to voltage at the input stage! 
@kijanki : look at the specs for the 462 amp! Both 2.1 and 4.2 volts both produce output wattage of 450!  So if the input voltage is slightly increased to 2.4 ala the Marantz 8802 you say that the wattage will go down to 1/4 of 450!!!! 
450watts 8ohms the voltage is 60volts according to ohm's law equations
V = I × R  and  P = V × I  or  V = (P × R )  and  P = V^2 / R

The voltage gain = 60 / 4.2 = 14.3
2.4volts x 14.3 = 34.3volts

34.3volts at 8ohms = 147watts

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It is exactly what it is.  His amplifier has 20dB gain for balanced input at 4ohm output posts.  20dB is10x.  When you input 4.2V input output becomes 10 x 4.2V = 42V  P = (42V^2) / 4 = 441W
At 2.1V input output becomes 21V   P = (21V^2) / 4 = 110.25W
@imhififan : OK! I can follow the math - but note that the specs for the 462 state "450 watts for either 2.1 or 4.2 volts"! That's way more than 147 watts according to your math!
look at the specs for the 462 amp! Both 2.1 and 4.2 volts both produce output wattage of 450!
Both 2.1V and 4.2V produce the same wattage of 450W but from different inputs (balanced and unbalanced) that have different gains.
Gain for this amp for 4ohm speaker is 26dB unbalanced and 20dB balanced.

@kijanki : go to the top and read the specs for the 462. Either RCA or XLR it outputs 450 watts for respectively 2.1 and 4.2 volts! Not 110.25 watts for 2.4 volts! 
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His pre outputs 2.4V for balanced output. His amp outputs 450W for 4.2V balanced input.

Amplifier’s output voltage will be a linear function of the input voltage. It has to be or amplifier will have huge distortions. Output power P = V^2 / R If you drive this balanced input with 2.4V instead of 4.2V output will become 24V instead of 42V and power will be (24^2) / 4 = 144W instead of (42^2) /4 = 441W
@kijanki : read the 462 specs again! 2.1 volts in produces 450 watts through the RCA's. 4.2 volts in through XLR's produces the same 450 watts because of the autoformer-coupled output stage. Even though gain is different from RCA vs. XLR!
Using autoformers in a present-day transistor amp is really backward engineering! Anyway the hot -or should I say cool- stuff is the interest and further development of class D amps. 
So what?  This amp has double gain at unbalanced input (26dB vs 20dB), for the output power to be 450W at nominal voltage at given input, but output voltage will be a linear function of input voltage at given input.  If you lower voltage at given input by 50% output voltage will become 50%.   1/2 of the output voltage produces 1/4 of the output power.
As for the output being always 450W. It is always 450W because for different speaker load transformer has different output voltage (amp has different gain). 8ohm speaker would normally produce half of the 4ohm speaker, but amp’s gain for 8ohm output is higher. We are not talking about this. We are talking about amp with speaker fixed to one output and pre fixed to one input.
Back to the topic of XLR adapters! Member almarg had a post on 2-20-2017 where he addressed this issue. He thought it was potentially a problem because of shunting pin 3 to ground at the RCA input since pin 3 is active! Possibly damaging the amp! I agree and say don't do it! 
A Jensen transformer is the best way to avoid the hot pin 3 problem - but at extra cost!
Success! EBay seller pinetreeaudio builds and sells a converter box using Jensen transformers for XLR -to-RCA : the Pine Tree Audio SE2B. $275 + $15 shipping. Build time 2 weeks. Located in Fitchburg, MA. Forget all the other cheap cr*p! This is the proper way to do the conversion! 
The SE2B looks real good in the photos, with its wood side panels and neat interior wiring with two Jensen transformers! Front panel has a pair of RCA jacks and a pair of XLR jacks.
I think that XLR/balanced outputs are over-rated! They are only useful if you need to run 10, 20, 30 ... feet cables! At one or two meters "No diffawrance" as the French chef said!
The benefit of balanced lines exists even if the connection is only 6". What the balanced line system was designed to do (and meets its design goals) is to eliminate ground loop hum (by ignoring ground) and eliminate cable colorations which also allows for long cables. Getting rid of cable interactions and ground loop (noise) issues is there even if the cable is only 6".
+1 Atmosphere.

My systems have been true balanced for 30+ years. I can hear the difference the same cable whether it's 0.5m or 1.5m