I understand the situation you are in.
Many of my clients take advantage of a positive sales proceed from selling a HDB apt to upgrade to a pte condo.
In your case on selling your HDB apt, your sales proceed is still positive of about $110k after taking a resale price say $530k less your outstanding loan of $176k and amount back to CPF O/A with interest est $230k and other misc fee.
On the part of buying a e-condo of $800k, strictly cash would be 1% option fee + 4% option exercise fee + Stamp fee of $18,600 + other misc fees. This would add up to abt $58,600+, of which the stamp fee of $18,600 can be reimbursed from CPF O/A later. The current cpf of $120k is sufficient for the 15% only.
If you are taking bank loan for financing the purchase of EC, you cant do contra. The dealing of EC is like pte apt transaction.
The combined income of $11k monthly which I do not see any issue getting a 80% bank loan not taking consideration your credits. Better that I help get my banker friend to do up a IPA for you first.
In my opinion, you can consider to sell your HDB apt first, get the sale proceed to better finance the EC later. To complete a HDB trasaction, it is about 4.5 months compared to a pte apt which is generally about 8-12 weeks.
I would be pleased to show you more details of the financial plan for your selling and buying. Do call me 9876 5130 to discuss further.