2 subs in series any affect on watts?

Will that stay the same as what?  You have two 8 ohm subs (series-wired dual 4 ohm coils) wired in parallel to make a 4 ohm load on the amp.  According to the above, the amp outputs 250 watts into 4 ohms.  So each sub will get 125 watts.  (If you had 8 of  these subs wired so that the total load was 4 ohms, each sub would get 31.25 watts.)

Use two DVC 2 ohm subs or two single 4 ohm subs, each with the capability of 250 watts continuous with that amplifier if you want 500 watts output.  This amp will output 500 watts if presented with a 2 ohm impedance load.

Both of your amplifiers are mono block (one channel) capable of outputting into a 2 ohm load for greatest output.  Greatest quality, for a little less SPL, can be achieved using a 4 ohm load.

Your single 4 ohm 10w0-4s may be parallel wired to make a 2 ohm load.  The TA2301 will output 300 watts, giving each sub 150 watts (slightly over their continuous handling of 125 watts).  Careful setup will allow you to do this.

The impedance of the load always affects the amplifier.  That's what causes it to make power.  As long as the amplifier is rated for the load you intend to put on it, it will perform.  Output is greater at lower impedance loads (2 ohm);  less at higher loads (4 ohms or above).

Continous power handling is just that - continuous, all day long.  It can be exceeded briefly, and probably will be during your setup and gain setting procedures.  I'm just saying that going into it knowing that the subs are rated slightly lower than the amp is rated, you would take extra precautions to set the gains.  But, who knows?  Maybe the sub is underrated and the amp is overrated...you don't really know for sure.

Search this forum for gain, or gain setting, if you need more answers on that.  What I said was pretty much a standard "...be a little extra careful there..." response when it's believed that your in an overpower situation.

As for the DVC subs, they are made for SQ anyway.  Don't feel that you need to run your amp full-out to power these, and loading the amp at 4 ohms is just fine.  A speaker doesn't need to be run at its thermal limit.  One watt of power will make some noise.  Remember that the ratings you see on a  amplifier is measured with a 4 ohm load, and the specs are better than the output at 2 ohms.  SQ setups use 4 ohm or higher.  You could wire these subs series/series and load the amp at 16 ohms if you wanted to.  In fact, it's not a bad experiment for anyone to try...in a lot of cases there is plenty of loudness.

The typical car audio consumer seems to think he has to "get every last watt out of the amplifier.  I paid for it!"

I'm not here to suggest what you buy or how you listen to your music.  If you have the gear already, set it up and see if it works for you.  You will probably be surprised at how loud you will get with a 4 ohm impedance when compared to the same gear at 2 ohms.  Roughly +3 db at the 2 ohm load, or if more because of added cabin gain, just slightly.

If you are just in the buying stage and don't have the amp (and you think that 250 watts won't be enough), the answer is simple:  buy a more powerful amplifier.  If you have the amp but don't yet have the speakers, buy the speakers configuration that will make the overall impedance what you want it to be.

BTW, I hope you are working on two different cars here.

Ah gee, I was afraid it was going there.  All I can say is, by the time you get that 5 cu ft box in there with those two 10W0-4s, vented and tuned to 27 Hz, he won't have a whole lotta room left over for the mix of whateverhehasonhand.

I'd build the box total inside volume of 5 cu ft.  Put in a 4" round port, 6.5" long (or 6" round X 17"L for super-quiet).  Feed these two subs 250 watts.  Great response and a surprisingly high level of decibels for a SQ setup at this power level, especially in a truck cab.  No excursion problems and very quiet port noise, he wouldn't hear anything but the music.

I can't (won't) be of any help when it comes to mixing up different subs.

No, I would go sealed with those.  For the two of them with up to 500 watts input, build anywhere from 2.8 cu ft to 4.5 cu ft.  The larger box is the smoother rolloff.  This is an SQ application and shouldn't be mixed with other subs.

Here is an SPL comparison chart.  The gray line is the box for the 10W0-4s as described earlier, with 250 watts input.    jlsplcompare.jpg

The other three lines compare the 10W3-D4s.  Yellow line shows SPL using a 2.8 cu ft box with 500 watts input.  Green is the larger 4.5 cu ft box with 500 watts.  Teal is the 4.5 cu ft box with 250 watts.