Newbie question

You would be amazed how loud just one watt can be. 
https://youtu.be/vaiEDYB5c9M

of course the 2500 wpc was a theoretical exaggeration,

It is not ADDITIVE. You would skip the amplifier part of the receiver,
remove the power tubes, connect no speakers to the receiver.

Only use the preamp section (IF the receiver has a way to do that), connect the preamp part of the receiver to your separate more powerful amplifier, i.e. 250 wpc.

Therefore, the answer to your question: You are correct: the receiver’s power rating makes no difference.

HOWEVER, as someone else pointed out, you may be quite surprised by how good a 30-35 wpc tube receiver sounds and how well it drives your speakers. 400 wpc speakers: Cerwin Vega’s were engineered to not burn out until you got over 400 wpc, they in no way need 400 wpc to get loud.

There was a LOT of competition in that 30-35 wpc range, engineers of each company going for the best, similar to the end of TT era 1984 when each company’s engineers tried to out-perform the others. That is why Vintage Receivers and TT’s are so desireable.

Most Vintage receivers have a tape recorder LOOP (out to tape, back in from tape), some have specific preamp out jacks, my Fisher 500c also has an optional reverb loop (jumpers on the deck can be removed) to use a reverb unit, OR ANY outboard device, i.e. a modern remote controlled device (like my Chase RLC-1 remote line controller). ANY Tape Loop can be used for ANY signal controlling device, or Preamp Out to processor, then back in via aux, any input.

The advantage:

ASSUMING your vintage receiver is in good shape, noise free, ...

Is that you retain all the ’old school’ features: bass and treble tone controls; balance; loudness; rumble filters; phase reverse; and some have a very useful mode switch that offers: stereo reverse; mono; l+r to L only .....

And receivers had TUNERS, FM, some AM and FM, most Stereo, very old ones Mono.

Happily, most have PHONO built in, many have two phono, some, like my mx100z has 3 phono in: 1 for old ceramic high strength signals, 2 for MM signals. Built-In MC phono very rare, perhaps none?

................................

PS

STOP LISTENING VERY LOUD! You will definitely regret it later because you will be damaging your hearing.

Receiver Tape (and most, "processor") outs are full line-level circuits; not affected by (in circuit before) volume, balance, tone, etc controls.     Worthless, far as an output source for an amplifier, outside of the receiver’s Selector/Source switch.      That’s: unless you want to add another volume control, or- have gains on the amp with which to control it’s output levels.

Royce, you are at the quantity not quality stage of freshman hi-fi. Have your fun but shortly you will learn that if you are really listening, you can’t play your music at high listening levels. Save your hearing, you only get one chance at it.