Capacitors for HP filters in tube amps recommendations?

Personally; I never paralleled capacitors, unless they were identical, to avoid any possible time-constant disparities.

That's not a concern... capacitors in parallel will just sum in value (like resistors in series)... the source and load won't see any difference. In fact there are good reasons to parallel capacitors. It's easier to match the values for left and right channels (more combinations) plus statistically you'll get a tighter tolerance than specification (although you'll need to parallel quite a few to make much difference). You can achieve higher capacitance than is commonly available for a particular dielectric (I have used 5 x 10uF wima for DC blocking). Also multiple smaller packages will have a larger surface area than a single large package so heat dissipation is better.
If you want to go down the route of matching your own for around $25 you can get a cap meter that will measure 1pF to 20,000uF although you might want to factor in a few precision caps to use for calibration.

I said, "personally".       You’re welcome to your opinion, if you have one regarding time-constants (which is to what I referred, but- you never addressed) and anyone else’s, that you value.

I was trying to be helpful, not make anyone wrong... I'm sorry if it didn't come across like that.

The time constant of an RC filter is the cutoff frequency, this is set by the product of the total resistance and total capacitance in the network. So the accuracy of those two values will determine how close you are likely to get to what you're aiming for. Low tolerance components (e.g 5%+) mean there's a larger margin of error in relation to the target cutoff point - sometimes that's important (e.g. RIAA filter), sometimes not so much (DC blocking filter).
Components can also change their value due to temperature changes, ageing and other factors. So when setting the time constant it's most important to select components with the required tolerance and stability which is mostly down to the dielectric (PP, polystyrene, polyester etc.) and the quality of manufacture.  Using caps in parallel doesn't affect any of these qualities providing they've got a good electrical connection.

No problem... even if you are tempted to try expensive capacitors, buy ten of these and compare. The only dialectric that may work better than polystyrene for this application is C0G/NP0 ceramic (definitely not any other type of ceramic) which is fine if you can solder surface mount but the through hole versions are ridiculously expensive.

100k and 80Hz requires .02uF, 30k and 175Hz .03uF.

 You parallel up .01uF caps (for caps in parallel you just sum the values), so five for each channel means $4.20 in capacitors.

All of the caps listed will be out performed by polystyrene in this application. Polypropylene are ideal when higher capacitance is required and the only other option would be electrolytic. I think there is a perception that more expensive must be better but in this case that is entirely wrong. If you want the best possible then look at the type of cap used in a top end phono amp in the RIAA section - there is no room for error in this application and any distortion will be massively amplified. I’ll put my money on them being polystyrene or NP0/C0G.

I guess the important factors in this application are that we're working at line level and we are setting time constants in the audible frequency range.

Line level means we don't need to worry about dealing with high currents, voltages or significant power dissipation (large packages are better at dissipating heat than small ones). But it also means that any distortion will be amplified by the following gain stages.

Setting the time constant means that we're attenuating a selection of frequencies, in this case ones we can hear so we're looking for precision and linearity (high linearity = low distortion).
If the actual capacitance deviates from the nominal capacitance then we'll find that the -3dB point is at a different frequency to that specified. In this case, assuming you can adjust the roll-off of your subs then the precision of the pair of filters (left and right) is not overly critical. However the precision between the filters (the difference between left and right) is critical and may well be audible if one channel rolls off at a different frequency to the other.
So we want to know that the capacitors on both channels are close in value but not so worried about how accurate that value is (in an RIAA filter both values are critical).

Linearity is a lack of distortion so the output of a linear component will closely resemble the input (in this case we are intentionally distorting the input by filtering out LF, but we want the audible frequencies to be unaffected). Linearity is measurable in Total Harmonic Distortion and there have been studies into the distortion characteristics of dielectrics,  if you want to learn more (and I completely understand if you don't) Doug Self has researched the topic in depth. C0G/NP0 and polystyrene caps can be considered free of distortion, polypropylene is very low distortion which can probably be said to be negligible, electrolytic is another matter.

So bearing this in mind...

Jupiter Copper Foil: I don't know the linearity of wax and paper but it can't be better than unmeasurable, so let's be generous and assume it's unmeasurable. Precision... the ones I found were 5%, okay but not great.

Clarity CMR: These are polypropylene so we know what we're dealing with. Precision is 3% which is better.

Miflex KFPM: Polypropylene and 2% precision.

Audyn True Copper: Couldn't even find out what the dielectric is, so let's assume it's unmeasurable again. 2% precision.

I couldn't find (admittedly I didn't try too hard) any detailed datasheets for the above. One thing they all have in common is that they are large, which means they can dissipate heat (which we don't need) but the size also means that the parasitic properties of the leads, foils etc are greater.

Polystyrene is available in 1% in a small package and has no distortion to speak of. So it's not streets ahead of the caps above but it will be better for this application (and that's without taking into account cost). Some of the exotics will probably be available in matched pairs which is an improvement... but still not better unless the matching is less than 1%.

I wrote more there than I meant to... I hope it's useful.

Wima is a good choice of PP capacitor, at line level I tend to use NP0/C0G for 10pF to 10nF, Wima MKP for 10nF to 10uF and try to avoid higher values in the signal path. Be aware the leads are short on the Wima caps so you may need to mount them on strip board as point to point soldering might be a bit fiddly although do-able.

I think you've found a solution that will work for you at a sensible price point... I didn't realise Wima made PP caps in 1% so I've learned something new too. I usually go for 5% as I use them for high pass filtering at sub-sonic levels, knowing they are available in tighter tolerances will come in handy I'm sure.