IIRC, DH has the Biz Platinum? A referral from that card will earn him 15k MR to his MR account. (Does he have the Business Gold Rewards or Business Gold card? That'll earn him 20k MR per referral.) Have DH log into the Amex Refer a Friend site with his account credentials to check what referral offers he has on his cards (and if he has several accounts, check them all). Copy the referral link from the card that gives the best referral bonus. Keep in mind, not all points are equal. 15k MR > 20k Hilton, etc. Also note that Amex MR cards are limited to 55k MR in referral bonuses per year. My feeling is, the best referral bonus is probably from DH's Biz Plat.
Copy the referral link, paste it in another browser or incognito window. If you're taken directly to the Biz Plat's application page, you don't want that, so find the banner/link to View All Cards with a Referral Offer, click Looking for a Personal Card, look through the different Amex products and find the Hilton Aspire (don't confuse it with the Ascend, etc.), click on Continue to Card Details and you'll be taken to the application page for the Aspire.
Why do you want the Hilton Aspire and who is going to use the Aspire benefits? The Aspire comes with, among many other things, complimentary Diamond status so if DH travels alone frequently, it may make sense for him to apply for the card and have that benefit attach to his Hilton account. The more info you provide, the better we can help.
Lain - DH has the Amex Biz Platinum (no co-brand) and a personal Gold (I am AU on the Gold, that is his oldest card).
We have his Amex linked to my Hilton rewards (he doesn't have). We travel as a family 4x a year to my hometown and stay Hilton (limited option, it is our favorite), and we took advantage of the recent Amex 50% extra transfer to Hilton and are using those points for a 5 night stay for a summer trip.
The benefits we would use:
$250 airline credit x2 (2019 and 2020) - value $500
need 15,000 more points for summer trip - value $150
weekend hotel night to be used in NYC - Value ~$300
Enough leftover points to cover some nights visiting family - value ~$500-$600
Diamond status and earning level for cash nights and possible perks during stays
possible resort credit for summer trip (have to see what's covered)
Airport lounge access- marginal bc not flying this year, but would use in Jan 2020
DH doesn't travel for work, I travel occasionally but on my work card.
We both have Global Access already
I have CSR as our primary travel card
We are not looking for luxury, we are looking to stretch out travel budget for family friendly trips